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Infectious Disease and Microbiology – Prostatitis
The term prostatitis encompasses several infectious and noninfectious disorders affecting the prostate gland. These include acute bacterial prostatitis, chronic bacterial prostatitis, chronic prostatitis with inflammatory and noninflammatory subtypes, asymptomatic inflammatory prostatitis, and granulomatous prostatitis. The most common form is chronic prostatitis/chronic pelvic pain syndrome, accounting for approximately 90% of cases. Overall prevalence of prostatitis ranges from 2–16% in the general population.
Genitourinary procedures are an important risk factor for acute bacterial prostatitis. Effective management of acute prostatitis reduces the risk of recurrent or chronic bacterial prostatitis. Bacterial prostatitis is associated with secretory dysfunction of the prostate. Prostatic secretions become more alkaline, affecting local antibiotic penetration, and there is a reduction in prostatic antibacterial factor, a zinc-containing antimicrobial polypeptide normally present in prostatic fluid.
Acute bacterial prostatitis is most commonly caused by typical uropathogens including Escherichia coli, other Enterobacteriaceae, Pseudomonas aeruginosa, and enterococci. Chronic bacterial prostatitis is usually caused by the same organisms. The inflammatory subtype of chronic prostatitis has an uncertain etiology, although some cases are associated with Chlamydia or Mycoplasma species. Leukocytes are present in expressed prostatic secretions. The noninflammatory subtype also has an unclear cause, though some patients demonstrate voiding dysfunction related to dyssynergy between bladder detrusor and internal sphincter muscles. Granulomatous prostatitis is rare and may follow acute bacterial prostatitis or result from infections such as tuberculosis, nontuberculous mycobacteria, cryptococcosis, blastomycosis, coccidioidomycosis, or histoplasmosis. In patients with AIDS, the prostate may serve as a persistent focus of cryptococcal infection.
Acute bacterial prostatitis should be suspected in any man presenting with symptoms consistent with urinary tract infection accompanied by perineal, pelvic, or lower back pain. Urinary frequency, dysuria, urgency, fever, and chills are common. Chronic bacterial prostatitis often presents with recurrent urinary tract infections caused by the same organism. Patients are frequently asymptomatic between episodes, although some report symptoms similar to chronic nonbacterial prostatitis.
Chronic prostatitis commonly presents with persistent or intermittent perineal, pelvic, lower back, scrotal, or inguinal pain. Urinary symptoms such as frequency, hesitancy, dribbling, urgency, and dysuria may occur. Erectile dysfunction and ejaculatory complaints are also common. Patients with asymptomatic inflammatory prostatitis have no genitourinary pain and are usually diagnosed incidentally during evaluation for infertility or elevated prostate-specific antigen levels.
Physical examination findings vary according to the type of prostatitis. In acute bacterial prostatitis, digital rectal examination performed gently may reveal an enlarged, tender prostate; vigorous examination should be avoided to prevent bacteremia. In chronic prostatitis, the prostate is generally normal on examination. Granulomatous prostatitis produces a firm, indurated prostate.
Laboratory evaluation includes urinalysis, urine culture, blood urea nitrogen, and creatinine measurements before initiating antibiotics. The classic diagnostic method is the four-glass Meares-Stamey test, which compares cultures from urethral urine (VB1), bladder urine (VB2), expressed prostatic secretions (EPS), and postmassage urine (VB3). Elevated bacterial colony counts in EPS or VB3 compared with VB1 suggest bacterial prostatitis. Presence of leukocytes in EPS or VB3 indicates prostatic inflammation. A simplified two-glass pre- and post-prostatic massage test is also commonly used. Imaging studies such as transrectal ultrasonography and CT scanning are useful for detecting prostatic stones and abscesses. Elderly patients with chronic prostatitis symptoms but no infection should undergo evaluation for bladder cancer with urine cytology, bladder ultrasonography, and cystoscopy if indicated.
Granulomatous prostatitis demonstrates granulomas with lipid-laden histiocytes, plasma cells, and multinucleated giant cells on histopathology. The differential diagnosis of prostatitis includes benign prostatic hyperplasia, bladder neck dysfunction, urethral stricture, prostatic calculi, and prostate cancer.
Treatment depends on the specific subtype. Mild acute bacterial prostatitis without nausea or vomiting is treated with oral fluoroquinolones such as levofloxacin or ciprofloxacin, or with trimethoprim-sulfamethoxazole (TMP-SMX), generally for 2–4 weeks. Moderate or severe illness requires parenteral antibiotics such as ampicillin plus gentamicin or intravenous fluoroquinolones until fever resolves, followed by oral therapy to complete a four-week course. Persistent infection may require retreatment for up to 12 weeks.
Chronic bacterial prostatitis requires antibiotics with good prostatic penetration. Preferred regimens include oral fluoroquinolones for four weeks or TMP-SMX for six weeks. Approximately one-third of patients achieve complete response, while others experience partial or no response. Extended antibiotic courses up to 12 weeks may be required. Suppressive therapy with daily TMP-SMX may be necessary in patients with recurrent infections.
There is no consistently effective therapy for chronic inflammatory prostatitis because the etiology is uncertain. A short trial of doxycycline or a macrolide is reasonable to target possible Chlamydia or Mycoplasma infection. If improvement occurs, treatment may continue for an additional 2–4 weeks. In noninflammatory prostatitis associated with voiding dysfunction, alpha-blockers such as tamsulosin, terazosin, or alfuzosin may provide benefit. Antibiotic therapy is not indicated for asymptomatic inflammatory prostatitis.
Supportive management of acute bacterial prostatitis includes stool softeners, analgesics, and antipyretics. Transurethral catheterization should be avoided because it may obstruct drainage of prostatic secretions; suprapubic catheterization is preferred if urinary retention occurs. In chronic prostatitis, hot sitz baths, anti-inflammatory medications, reassurance, and encouragement of sexual activity may improve symptoms. Some patients with pelvic floor tension myalgia benefit from pelvic floor exercises, diathermy, or diazepam. Prostatic massage, oral zinc, and vitamin supplements have unproven benefit.
Surgical intervention may be necessary in chronic bacterial prostatitis complicated by recurrent urinary tract infections despite suppressive therapy or by infected prostatic calculi. Transurethral or open prostate resection may be considered in selected patients.
Follow-up urine cultures should be obtained approximately 14 days after completing treatment for acute bacterial prostatitis. Complications of acute bacterial prostatitis include prostatic abscess, prostatic infarction, bacteremia, progression to chronic bacterial prostatitis, and granulomatous prostatitis.
The term prostatitis encompasses several infectious and noninfectious disorders affecting the prostate gland. These include acute bacterial prostatitis, chronic bacterial prostatitis, chronic prostatitis with inflammatory and noninflammatory subtypes, asymptomatic inflammatory prostatitis, and granulomatous prostatitis. The most common form is chronic prostatitis/chronic pelvic pain syndrome, accounting for approximately 90% of cases. Overall prevalence of prostatitis ranges from 2–16% in the general population.
Genitourinary procedures are an important risk factor for acute bacterial prostatitis. Effective management of acute prostatitis reduces the risk of recurrent or chronic bacterial prostatitis. Bacterial prostatitis is associated with secretory dysfunction of the prostate. Prostatic secretions become more alkaline, affecting local antibiotic penetration, and there is a reduction in prostatic antibacterial factor, a zinc-containing antimicrobial polypeptide normally present in prostatic fluid.
Acute bacterial prostatitis is most commonly caused by typical uropathogens including Escherichia coli, other Enterobacteriaceae, Pseudomonas aeruginosa, and enterococci. Chronic bacterial prostatitis is usually caused by the same organisms. The inflammatory subtype of chronic prostatitis has an uncertain etiology, although some cases are associated with Chlamydia or Mycoplasma species. Leukocytes are present in expressed prostatic secretions. The noninflammatory subtype also has an unclear cause, though some patients demonstrate voiding dysfunction related to dyssynergy between bladder detrusor and internal sphincter muscles. Granulomatous prostatitis is rare and may follow acute bacterial prostatitis or result from infections such as tuberculosis, nontuberculous mycobacteria, cryptococcosis, blastomycosis, coccidioidomycosis, or histoplasmosis. In patients with AIDS, the prostate may serve as a persistent focus of cryptococcal infection.
Acute bacterial prostatitis should be suspected in any man presenting with symptoms consistent with urinary tract infection accompanied by perineal, pelvic, or lower back pain. Urinary frequency, dysuria, urgency, fever, and chills are common. Chronic bacterial prostatitis often presents with recurrent urinary tract infections caused by the same organism. Patients are frequently asymptomatic between episodes, although some report symptoms similar to chronic nonbacterial prostatitis.
Chronic prostatitis commonly presents with persistent or intermittent perineal, pelvic, lower back, scrotal, or inguinal pain. Urinary symptoms such as frequency, hesitancy, dribbling, urgency, and dysuria may occur. Erectile dysfunction and ejaculatory complaints are also common. Patients with asymptomatic inflammatory prostatitis have no genitourinary pain and are usually diagnosed incidentally during evaluation for infertility or elevated prostate-specific antigen levels.
Physical examination findings vary according to the type of prostatitis. In acute bacterial prostatitis, digital rectal examination performed gently may reveal an enlarged, tender prostate; vigorous examination should be avoided to prevent bacteremia. In chronic prostatitis, the prostate is generally normal on examination. Granulomatous prostatitis produces a firm, indurated prostate.
Laboratory evaluation includes urinalysis, urine culture, blood urea nitrogen, and creatinine measurements before initiating antibiotics. The classic diagnostic method is the four-glass Meares-Stamey test, which compares cultures from urethral urine (VB1), bladder urine (VB2), expressed prostatic secretions (EPS), and postmassage urine (VB3). Elevated bacterial colony counts in EPS or VB3 compared with VB1 suggest bacterial prostatitis. Presence of leukocytes in EPS or VB3 indicates prostatic inflammation. A simplified two-glass pre- and post-prostatic massage test is also commonly used. Imaging studies such as transrectal ultrasonography and CT scanning are useful for detecting prostatic stones and abscesses. Elderly patients with chronic prostatitis symptoms but no infection should undergo evaluation for bladder cancer with urine cytology, bladder ultrasonography, and cystoscopy if indicated.
Granulomatous prostatitis demonstrates granulomas with lipid-laden histiocytes, plasma cells, and multinucleated giant cells on histopathology. The differential diagnosis of prostatitis includes benign prostatic hyperplasia, bladder neck dysfunction, urethral stricture, prostatic calculi, and prostate cancer.
Treatment depends on the specific subtype. Mild acute bacterial prostatitis without nausea or vomiting is treated with oral fluoroquinolones such as levofloxacin or ciprofloxacin, or with trimethoprim-sulfamethoxazole (TMP-SMX), generally for 2–4 weeks. Moderate or severe illness requires parenteral antibiotics such as ampicillin plus gentamicin or intravenous fluoroquinolones until fever resolves, followed by oral therapy to complete a four-week course. Persistent infection may require retreatment for up to 12 weeks.
Chronic bacterial prostatitis requires antibiotics with good prostatic penetration. Preferred regimens include oral fluoroquinolones for four weeks or TMP-SMX for six weeks. Approximately one-third of patients achieve complete response, while others experience partial or no response. Extended antibiotic courses up to 12 weeks may be required. Suppressive therapy with daily TMP-SMX may be necessary in patients with recurrent infections.
There is no consistently effective therapy for chronic inflammatory prostatitis because the etiology is uncertain. A short trial of doxycycline or a macrolide is reasonable to target possible Chlamydia or Mycoplasma infection. If improvement occurs, treatment may continue for an additional 2–4 weeks. In noninflammatory prostatitis associated with voiding dysfunction, alpha-blockers such as tamsulosin, terazosin, or alfuzosin may provide benefit. Antibiotic therapy is not indicated for asymptomatic inflammatory prostatitis.
Supportive management of acute bacterial prostatitis includes stool softeners, analgesics, and antipyretics. Transurethral catheterization should be avoided because it may obstruct drainage of prostatic secretions; suprapubic catheterization is preferred if urinary retention occurs. In chronic prostatitis, hot sitz baths, anti-inflammatory medications, reassurance, and encouragement of sexual activity may improve symptoms. Some patients with pelvic floor tension myalgia benefit from pelvic floor exercises, diathermy, or diazepam. Prostatic massage, oral zinc, and vitamin supplements have unproven benefit.
Surgical intervention may be necessary in chronic bacterial prostatitis complicated by recurrent urinary tract infections despite suppressive therapy or by infected prostatic calculi. Transurethral or open prostate resection may be considered in selected patients.
Follow-up urine cultures should be obtained approximately 14 days after completing treatment for acute bacterial prostatitis. Complications of acute bacterial prostatitis include prostatic abscess, prostatic infarction, bacteremia, progression to chronic bacterial prostatitis, and granulomatous prostatitis.
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Infectious Disease and Microbiology – Progressive Multifocal Leukoencephalopathy
Progressive multifocal leukoencephalopathy (PML) is a rare, subacute demyelinating disease of the brain white matter caused by primary infection or reactivation of JC virus (JCV). First identified in 1958, PML primarily affects patients with AIDS or other forms of impaired cell-mediated immunity. The disease is characterized by rapidly progressive focal neurologic deficits and is often fatal. PML is considered an AIDS-defining illness.
The incidence of PML increased significantly during the HIV/AIDS epidemic but declined after the widespread introduction of highly active antiretroviral therapy (HAART). Before the HIV era, reported deaths due to PML were approximately 1.5 per 10 million persons in 1974, increasing to 6.1 per 10 million by 1987. Among untreated HIV-positive individuals, 1–4% may develop PML. In 1992, approximately 2% of HIV-related deaths were attributed to PML. A Danish study demonstrated declining incidence rates following the introduction of HAART: 3.3 cases per 1000 patient-years during the pre-HAART era (1995–1996), 1.8 cases per 1000 patient-years during early HAART (1997–1999), and 1.3 cases per 1000 patient-years during late HAART (2000–2006).
JC virus infection is extremely common in the general population. Seroprevalence among adults in the United States and Europe ranges from 60–80%. Primary infection usually occurs during childhood between 10 and 14 years of age and is generally asymptomatic. Although most individuals remain asymptomatic carriers, active viral replication is more commonly observed in immunocompromised patients, particularly those infected with HIV. Asymptomatic urinary shedding of JCV and BK virus has been documented in immunosuppressed individuals, pregnant women, and the elderly.
The most important risk factor for PML is advanced HIV infection, especially with CD4 counts below 100/mm³. More than 60% of PML cases occur in this setting. Other risk factors include congenital or acquired immunodeficiency, organ transplantation, hematologic malignancies, chronic corticosteroid therapy, and immunosuppressive treatment for autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and sarcoidosis. Rare cases have occurred without identifiable immunodeficiency. Cases have also been reported in patients with multiple sclerosis or Crohn’s disease receiving natalizumab therapy, with risk increasing with prolonged treatment duration.
The exact mode of transmission and incubation period of JCV are not fully understood. Primary infection has been documented in renal transplant recipients receiving organs from seropositive donors. In PML, the virus infects oligodendrocytes within the central nervous system, leading to widespread demyelination. Neurologic deterioration progresses rapidly over weeks and typically occurs without signs of increased intracranial pressure. In some HIV-positive patients, initiation of HAART may paradoxically trigger inflammatory PML as part of immune reconstitution inflammatory syndrome (IRIS).
JC virus is a DNA virus belonging to the family Papovaviridae and genus Polyomavirus. Although BK virus is another known human polyomavirus, it is not associated with PML.
Patients with PML typically present without constitutional symptoms such as fever. Common manifestations at presentation include hemiparesis, visual field deficits such as homonymous hemianopia, cognitive impairment, aphasia, ataxia, cranial nerve deficits, sensory abnormalities, seizures, confusion, personality changes, and dementia. The spinal cord is usually spared. As the disease progresses, patients may develop profound neurologic deficits including cortical blindness, quadriparesis, severe dementia, coma, and marked motor weakness. Clinical manifestations are often more severe than expected from imaging or pathological findings. The presentation is similar in both HIV-positive and HIV-negative individuals.
The diagnostic gold standard is demonstration of JC virus antigen or genomic DNA within brain tissue combined with characteristic pathological findings. Detection methods include immunocytochemistry, in situ hybridization, and polymerase chain reaction (PCR). Because brain biopsy carries substantial risk, PCR detection of JCV DNA in cerebrospinal fluid is the preferred diagnostic test. In patients not receiving HAART, PCR sensitivity ranges from 72–92% and specificity from 92–100%. Sensitivity decreases after initiation of HAART because viral replication declines. Cerebrospinal fluid findings are nonspecific and may include pleocytosis, elevated IgG, and oligoclonal bands. Serologic testing is generally not useful. Viral culture is impractical because JCV grows very slowly and susceptible cell lines are difficult to obtain.
Imaging studies play a central role in diagnosis. CT scans typically demonstrate hypodense, non-enhancing subcortical white matter lesions without edema or mass effect, often involving the periventricular regions, centrum semiovale, parieto-occipital areas, and cerebellum. MRI is more sensitive and usually reveals multiple asymmetric subcortical white matter lesions with high T2 signal intensity. Inflammatory PML is characterized by contrast-enhancing lesions. Electroencephalography may show focal or diffuse slowing, and abnormalities may occasionally precede CT changes.
Pathologically, PML results from direct JCV infection and destruction of oligodendrocytes, leading to multifocal demyelination throughout the central nervous system with minimal inflammatory response. Reactive gliosis, bizarre astrocytes with lobulated nuclei, and lipid-laden macrophages are commonly observed. The cerebral hemispheres, cerebellum, and brainstem may all be affected, while spinal cord involvement is uncommon. Electron microscopy reveals polyomavirus inclusions within enlarged oligodendrocyte nuclei.
The differential diagnosis includes HIV encephalopathy, opportunistic CNS infections such as cytomegalovirus, neurosyphilis, cryptococcosis, tuberculous meningitis, and toxoplasmosis, as well as primary CNS lymphoma and Kaposi’s sarcoma. Other considerations include acute multiple sclerosis, acute hemorrhagic leukoencephalitis, herpes simplex encephalitis, multifocal varicella-zoster leukoencephalitis, postinfectious encephalomyelitis, and cyclosporine-induced neurotoxicity.
There is currently no specific antiviral therapy for PML. In HIV-positive patients, the primary treatment strategy is aggressive antiretroviral therapy to restore immune function. Patients with dementia may require supervised medication administration to ensure adherence. In individuals with PML related to immunosuppressive therapy, reduction or discontinuation of immunosuppressive agents is recommended whenever possible. Intravenous or intrathecal cytarabine may provide some benefit in patients with hematologic malignancies, although evidence is limited. Cidofovir has not demonstrated clinical benefit. Corticosteroids may be useful in inflammatory PML associated with immune reconstitution. In cases associated with natalizumab therapy, plasma exchange combined with discontinuation of natalizumab has been attempted.
Patients require frequent neurologic and clinical follow-up to monitor for disease progression or recurrence. HIV-positive patients also require ongoing monitoring of HIV disease activity and immune status.
The prognosis of PML remains poor. Death typically occurs within approximately six months of diagnosis. However, some HIV-positive patients may experience spontaneous fluctuations or prolonged survival over several years, particularly if immune function improves substantially with aggressive antiretroviral therapy.
Progressive multifocal leukoencephalopathy (PML) is a rare, subacute demyelinating disease of the brain white matter caused by primary infection or reactivation of JC virus (JCV). First identified in 1958, PML primarily affects patients with AIDS or other forms of impaired cell-mediated immunity. The disease is characterized by rapidly progressive focal neurologic deficits and is often fatal. PML is considered an AIDS-defining illness.
The incidence of PML increased significantly during the HIV/AIDS epidemic but declined after the widespread introduction of highly active antiretroviral therapy (HAART). Before the HIV era, reported deaths due to PML were approximately 1.5 per 10 million persons in 1974, increasing to 6.1 per 10 million by 1987. Among untreated HIV-positive individuals, 1–4% may develop PML. In 1992, approximately 2% of HIV-related deaths were attributed to PML. A Danish study demonstrated declining incidence rates following the introduction of HAART: 3.3 cases per 1000 patient-years during the pre-HAART era (1995–1996), 1.8 cases per 1000 patient-years during early HAART (1997–1999), and 1.3 cases per 1000 patient-years during late HAART (2000–2006).
JC virus infection is extremely common in the general population. Seroprevalence among adults in the United States and Europe ranges from 60–80%. Primary infection usually occurs during childhood between 10 and 14 years of age and is generally asymptomatic. Although most individuals remain asymptomatic carriers, active viral replication is more commonly observed in immunocompromised patients, particularly those infected with HIV. Asymptomatic urinary shedding of JCV and BK virus has been documented in immunosuppressed individuals, pregnant women, and the elderly.
The most important risk factor for PML is advanced HIV infection, especially with CD4 counts below 100/mm³. More than 60% of PML cases occur in this setting. Other risk factors include congenital or acquired immunodeficiency, organ transplantation, hematologic malignancies, chronic corticosteroid therapy, and immunosuppressive treatment for autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and sarcoidosis. Rare cases have occurred without identifiable immunodeficiency. Cases have also been reported in patients with multiple sclerosis or Crohn’s disease receiving natalizumab therapy, with risk increasing with prolonged treatment duration.
The exact mode of transmission and incubation period of JCV are not fully understood. Primary infection has been documented in renal transplant recipients receiving organs from seropositive donors. In PML, the virus infects oligodendrocytes within the central nervous system, leading to widespread demyelination. Neurologic deterioration progresses rapidly over weeks and typically occurs without signs of increased intracranial pressure. In some HIV-positive patients, initiation of HAART may paradoxically trigger inflammatory PML as part of immune reconstitution inflammatory syndrome (IRIS).
JC virus is a DNA virus belonging to the family Papovaviridae and genus Polyomavirus. Although BK virus is another known human polyomavirus, it is not associated with PML.
Patients with PML typically present without constitutional symptoms such as fever. Common manifestations at presentation include hemiparesis, visual field deficits such as homonymous hemianopia, cognitive impairment, aphasia, ataxia, cranial nerve deficits, sensory abnormalities, seizures, confusion, personality changes, and dementia. The spinal cord is usually spared. As the disease progresses, patients may develop profound neurologic deficits including cortical blindness, quadriparesis, severe dementia, coma, and marked motor weakness. Clinical manifestations are often more severe than expected from imaging or pathological findings. The presentation is similar in both HIV-positive and HIV-negative individuals.
The diagnostic gold standard is demonstration of JC virus antigen or genomic DNA within brain tissue combined with characteristic pathological findings. Detection methods include immunocytochemistry, in situ hybridization, and polymerase chain reaction (PCR). Because brain biopsy carries substantial risk, PCR detection of JCV DNA in cerebrospinal fluid is the preferred diagnostic test. In patients not receiving HAART, PCR sensitivity ranges from 72–92% and specificity from 92–100%. Sensitivity decreases after initiation of HAART because viral replication declines. Cerebrospinal fluid findings are nonspecific and may include pleocytosis, elevated IgG, and oligoclonal bands. Serologic testing is generally not useful. Viral culture is impractical because JCV grows very slowly and susceptible cell lines are difficult to obtain.
Imaging studies play a central role in diagnosis. CT scans typically demonstrate hypodense, non-enhancing subcortical white matter lesions without edema or mass effect, often involving the periventricular regions, centrum semiovale, parieto-occipital areas, and cerebellum. MRI is more sensitive and usually reveals multiple asymmetric subcortical white matter lesions with high T2 signal intensity. Inflammatory PML is characterized by contrast-enhancing lesions. Electroencephalography may show focal or diffuse slowing, and abnormalities may occasionally precede CT changes.
Pathologically, PML results from direct JCV infection and destruction of oligodendrocytes, leading to multifocal demyelination throughout the central nervous system with minimal inflammatory response. Reactive gliosis, bizarre astrocytes with lobulated nuclei, and lipid-laden macrophages are commonly observed. The cerebral hemispheres, cerebellum, and brainstem may all be affected, while spinal cord involvement is uncommon. Electron microscopy reveals polyomavirus inclusions within enlarged oligodendrocyte nuclei.
The differential diagnosis includes HIV encephalopathy, opportunistic CNS infections such as cytomegalovirus, neurosyphilis, cryptococcosis, tuberculous meningitis, and toxoplasmosis, as well as primary CNS lymphoma and Kaposi’s sarcoma. Other considerations include acute multiple sclerosis, acute hemorrhagic leukoencephalitis, herpes simplex encephalitis, multifocal varicella-zoster leukoencephalitis, postinfectious encephalomyelitis, and cyclosporine-induced neurotoxicity.
There is currently no specific antiviral therapy for PML. In HIV-positive patients, the primary treatment strategy is aggressive antiretroviral therapy to restore immune function. Patients with dementia may require supervised medication administration to ensure adherence. In individuals with PML related to immunosuppressive therapy, reduction or discontinuation of immunosuppressive agents is recommended whenever possible. Intravenous or intrathecal cytarabine may provide some benefit in patients with hematologic malignancies, although evidence is limited. Cidofovir has not demonstrated clinical benefit. Corticosteroids may be useful in inflammatory PML associated with immune reconstitution. In cases associated with natalizumab therapy, plasma exchange combined with discontinuation of natalizumab has been attempted.
Patients require frequent neurologic and clinical follow-up to monitor for disease progression or recurrence. HIV-positive patients also require ongoing monitoring of HIV disease activity and immune status.
The prognosis of PML remains poor. Death typically occurs within approximately six months of diagnosis. However, some HIV-positive patients may experience spontaneous fluctuations or prolonged survival over several years, particularly if immune function improves substantially with aggressive antiretroviral therapy.
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Infectious disease and microbiology – Pertussis
Pertussis, commonly known as whooping cough, is a highly contagious respiratory infection caused primarily by Bordetella pertussis and less commonly by Bordetella parapertussis. Although vaccination has greatly reduced the disease burden in children, pertussis remains a worldwide health problem, especially among adolescents and adults, who may unknowingly transmit the infection to vulnerable infants.
The incidence among vaccinated children is significantly lower compared with unvaccinated populations, but outbreaks still occur. Infection rates remain considerable among older children and young adults due to waning immunity over time. Adults and older siblings often serve as reservoirs for transmission to infants who are either unvaccinated or incompletely vaccinated.
Prevention relies mainly on routine immunization, typically given in combination with diphtheria and tetanus vaccines during infancy and childhood, with booster doses later in life. Prophylactic antibiotics are recommended for close household contacts once a case is identified. Macrolides or trimethoprim-sulfamethoxazole are commonly used for this purpose.
The pathogenesis of pertussis involves colonization of the respiratory epithelium by the organism. Bordetella produces several toxins, including pertussis toxin and tracheal cytotoxin, which damage respiratory tissues and contribute to the characteristic prolonged cough. Inflammatory mediators such as bradykinin may also play a role in the persistent paroxysmal coughing spells.
After an incubation period of about 7–10 days, the disease classically progresses through three stages. The catarrhal phase resembles a mild upper respiratory infection with rhinorrhea, low-grade fever, and conjunctivitis. This is followed by the paroxysmal phase, characterized by severe bouts of coughing that may last several weeks. Finally, during the convalescent phase, coughing gradually improves over 1–2 weeks.
In young unvaccinated children, the hallmark finding is the “whoop,” a high-pitched inspiratory sound following a coughing fit. These episodes may be associated with cyanosis and vomiting. Adults and previously vaccinated individuals often present atypically with only a prolonged cough, which contributes to underdiagnosis and ongoing transmission.
Diagnosis is confirmed through culture or PCR testing of nasopharyngeal specimens, especially during the first two weeks of illness. Marked lymphocytosis may be present during the paroxysmal phase. Serologic testing demonstrating high antibody titers or a significant rise in antibodies can also support the diagnosis. Chest radiographs may show perihilar infiltrates, atelectasis, or consolidation in complicated cases.
Treatment is primarily supportive, especially in infants younger than one year, who are at greatest risk of severe disease. Antibiotics are mainly used to eradicate the organism and reduce transmission rather than shorten the duration of cough once the paroxysmal phase has begun. Macrolides such as azithromycin, clarithromycin, and erythromycin are the preferred agents. Trimethoprim-sulfamethoxazole is an alternative for patients who cannot tolerate macrolides.
Hospitalization may be required for infants, unvaccinated children, or patients with severe disease. Despite modern therapy, pertussis can lead to serious complications, particularly in infants, including pneumonia, apnea, seizures, encephalopathy, and death. Severe coughing can also cause subconjunctival hemorrhage, pneumothorax, rib fractures, rectal prolapse, and intracranial hemorrhage. Prognosis is generally excellent after recovery, although mortality remains highest among infants too young to be vaccinated.
Pertussis, commonly known as whooping cough, is a highly contagious respiratory infection caused primarily by Bordetella pertussis and less commonly by Bordetella parapertussis. Although vaccination has greatly reduced the disease burden in children, pertussis remains a worldwide health problem, especially among adolescents and adults, who may unknowingly transmit the infection to vulnerable infants.
The incidence among vaccinated children is significantly lower compared with unvaccinated populations, but outbreaks still occur. Infection rates remain considerable among older children and young adults due to waning immunity over time. Adults and older siblings often serve as reservoirs for transmission to infants who are either unvaccinated or incompletely vaccinated.
Prevention relies mainly on routine immunization, typically given in combination with diphtheria and tetanus vaccines during infancy and childhood, with booster doses later in life. Prophylactic antibiotics are recommended for close household contacts once a case is identified. Macrolides or trimethoprim-sulfamethoxazole are commonly used for this purpose.
The pathogenesis of pertussis involves colonization of the respiratory epithelium by the organism. Bordetella produces several toxins, including pertussis toxin and tracheal cytotoxin, which damage respiratory tissues and contribute to the characteristic prolonged cough. Inflammatory mediators such as bradykinin may also play a role in the persistent paroxysmal coughing spells.
After an incubation period of about 7–10 days, the disease classically progresses through three stages. The catarrhal phase resembles a mild upper respiratory infection with rhinorrhea, low-grade fever, and conjunctivitis. This is followed by the paroxysmal phase, characterized by severe bouts of coughing that may last several weeks. Finally, during the convalescent phase, coughing gradually improves over 1–2 weeks.
In young unvaccinated children, the hallmark finding is the “whoop,” a high-pitched inspiratory sound following a coughing fit. These episodes may be associated with cyanosis and vomiting. Adults and previously vaccinated individuals often present atypically with only a prolonged cough, which contributes to underdiagnosis and ongoing transmission.
Diagnosis is confirmed through culture or PCR testing of nasopharyngeal specimens, especially during the first two weeks of illness. Marked lymphocytosis may be present during the paroxysmal phase. Serologic testing demonstrating high antibody titers or a significant rise in antibodies can also support the diagnosis. Chest radiographs may show perihilar infiltrates, atelectasis, or consolidation in complicated cases.
Treatment is primarily supportive, especially in infants younger than one year, who are at greatest risk of severe disease. Antibiotics are mainly used to eradicate the organism and reduce transmission rather than shorten the duration of cough once the paroxysmal phase has begun. Macrolides such as azithromycin, clarithromycin, and erythromycin are the preferred agents. Trimethoprim-sulfamethoxazole is an alternative for patients who cannot tolerate macrolides.
Hospitalization may be required for infants, unvaccinated children, or patients with severe disease. Despite modern therapy, pertussis can lead to serious complications, particularly in infants, including pneumonia, apnea, seizures, encephalopathy, and death. Severe coughing can also cause subconjunctival hemorrhage, pneumothorax, rib fractures, rectal prolapse, and intracranial hemorrhage. Prognosis is generally excellent after recovery, although mortality remains highest among infants too young to be vaccinated.
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Infectious Disease and Microbiology – Poliomyelitis
Poliomyelitis is an acute viral infection caused by a small RNA enterovirus known as poliovirus. Most infections are asymptomatic or inapparent. However, in approximately 1% of infected individuals, the virus invades the central nervous system and causes varying degrees of paralysis. Poliomyelitis was once a major global cause of disability and death, but widespread vaccination has dramatically reduced disease incidence worldwide.
No cases of wild-type poliovirus infection have been reported in the United States since 1979. Before eradication efforts intensified, vaccine-derived polioviruses were reported at an average rate of 8–10 cases annually until 1998. Humans are the only known reservoir, and there are no chronic carriers or animal reservoirs. Wild-type polioviruses, vaccine strains from oral poliovirus vaccine (OPV), and vaccine-derived polioviruses may circulate in susceptible populations. By 2005, indigenous transmission of wild-type poliovirus types 1 and 3 had been eliminated from all but four countries: Afghanistan, India, Nigeria, and Pakistan. Wild-type poliovirus type 2 transmission has been globally interrupted. Despite major eradication efforts, outbreaks continue to occur after importation of wild-type virus into previously polio-free countries.
Risk factors for poliovirus infection include overcrowding and poor sanitation, both of which facilitate fecal–oral transmission. Factors associated with increased risk of paralytic disease include B-cell immunodeficiency, strenuous exercise during the early phase of illness, intramuscular injections into affected limbs, and recent tonsillectomy.
Two vaccines are available for prevention: the inactivated poliomyelitis vaccine (IPV) and the live attenuated oral poliomyelitis vaccine (OPV). IPV is administered parenterally and contains all three poliovirus serotypes. It produces excellent systemic immunity, with nearly 100% seroconversion after the third dose, but induces limited intestinal immunity, allowing asymptomatic infection and viral shedding. OPV, used mainly in developing countries, is inexpensive and easy to administer. It induces strong intestinal immunity and enhances herd immunity because vaccinated individuals shed attenuated virus in stool. However, OPV carries a rare risk of vaccine-derived paralytic poliomyelitis, especially in immunocompromised individuals. For this reason, all-IPV schedules are now recommended in the United States and Europe. The routine childhood IPV schedule includes four doses administered at 2 months, 4 months, 6–18 months, and 4–6 years of age.
Humans are the only known reservoir for poliovirus. In developing countries, the fecal–oral route is the principal mode of transmission, while respiratory droplet spread is relatively more important in developed countries. After entering the body, the virus initially infects intestinal epithelial cells and replicates within local lymphatic tissue, causing minor viremia. Infection may terminate at this stage or progress to major viremia involving reticuloendothelial tissues. Central nervous system invasion occurs by retrograde axonal transport from muscle to nerve and spinal cord. Poliovirus preferentially destroys anterior horn cells and motor nuclei within the spinal cord, pons, and medulla, leading to flaccid paralysis affecting the axial muscles, limbs, cranial nerves, or brainstem.
Poliovirus belongs to the family Picornaviridae and genus Enterovirus. Three serotypes exist: types 1, 2, and 3. Infection with one serotype confers immunity only to that serotype, with little cross-protection against the others. Prior to widespread vaccination, serotype 1 caused most paralytic cases.
The incubation period from exposure to the onset of minor illness is approximately 9–12 days, while paralysis generally develops after 11–17 days. Approximately 95% of infections are asymptomatic and detectable only by serology or viral isolation. Abortive poliomyelitis, also known as minor illness, occurs in 4–8% of infected individuals and presents as a nonspecific upper respiratory tract infection with sore throat, low-grade fever, abdominal pain, and diarrhea. Recovery is rapid and complete.
Nonparalytic poliomyelitis occurs in about 1% of infections and is characterized by signs of aseptic meningitis, including neck and back stiffness and pain, following a nonspecific febrile illness. Symptoms usually resolve within 2–10 days.
Spinal paralytic poliomyelitis represents the major form of disease and occurs in approximately 0.1% of infections. Patients develop localized muscle pain and fasciculations several days after the minor illness stage. Fever returns, followed by the rapid onset of asymmetric flaccid paralysis, predominantly involving proximal muscles. Lower extremities are more commonly affected than upper extremities. Sensory loss is typically absent, but deep tendon reflexes are lost. Severe cases may progress to quadriplegia and bulbar involvement.
Bulbar paralytic poliomyelitis involves cranial nerve nuclei, particularly cranial nerves IX and X, leading to dysphagia, nasal speech, and respiratory compromise. Bulbar involvement occurs in 5–35% of paralytic cases and may progress rapidly over several days or even hours. Mixed spinal and bulbar involvement is common. A rare form, polioencephalitis, occurs primarily in children and may present with seizures.
Laboratory evaluation commonly demonstrates cerebrospinal fluid pleocytosis similar to other causes of aseptic meningitis. Poliovirus can be isolated from pharyngeal secretions during the first week of illness and from stool specimens for several weeks. Isolation from cerebrospinal fluid is uncommon. Serologic testing with acute and convalescent sera can confirm infection through neutralizing antibody responses against all three serotypes. Molecular genotyping is important in distinguishing wild-type from vaccine-derived strains.
Neuroimaging studies such as CT or MRI are mainly used to exclude alternative causes of paralysis. MRI may reveal T2-weighted hyperintensities involving the bilateral anterior horn cells. Pathological examination demonstrates neuronal destruction and inflammatory lesions affecting the gray matter of the anterior horns and motor nuclei of the brainstem.
The differential diagnosis includes other enteroviral infections, botulism, West Nile virus infection, transverse myelitis, epidural spinal lesions, tick paralysis, Guillain-Barré syndrome, neuropathies, and stroke. Guillain-Barré syndrome is distinguished by its symmetric ascending paralysis.
There is no specific antiviral therapy for poliomyelitis. Management is primarily supportive. During the acute phase, hospitalization is required for monitoring and supportive care. Strict bed rest is essential to minimize progression of paralysis. Positive pressure ventilation may be necessary when respiratory muscle weakness causes reduced vital capacity. Physical therapy should begin promptly once progression of paralysis has stopped in order to preserve muscle function and prevent contractures. Patients should consume a diet rich in fiber because constipation is common.
The prognosis varies according to disease severity. Bulbar poliomyelitis carries the highest mortality rate, approaching 60%. Approximately two-thirds of patients with paralytic disease are left with some degree of permanent weakness. Complete recovery is uncommon in patients with severe paralysis. Survivors of bulbar paralysis often show substantial improvement within 10 days, and long-term outcome can usually be estimated after one month.
Complications of paralytic poliomyelitis include respiratory failure, gastric dilatation, and paralytic ileus. Years after recovery, some patients develop post-poliomyelitis syndrome, characterized by gradual onset of muscle weakness, pain, fatigue, and muscle atrophy affecting previously involved muscles. This syndrome typically appears 25–35 years after the initial infection.
Poliomyelitis is an acute viral infection caused by a small RNA enterovirus known as poliovirus. Most infections are asymptomatic or inapparent. However, in approximately 1% of infected individuals, the virus invades the central nervous system and causes varying degrees of paralysis. Poliomyelitis was once a major global cause of disability and death, but widespread vaccination has dramatically reduced disease incidence worldwide.
No cases of wild-type poliovirus infection have been reported in the United States since 1979. Before eradication efforts intensified, vaccine-derived polioviruses were reported at an average rate of 8–10 cases annually until 1998. Humans are the only known reservoir, and there are no chronic carriers or animal reservoirs. Wild-type polioviruses, vaccine strains from oral poliovirus vaccine (OPV), and vaccine-derived polioviruses may circulate in susceptible populations. By 2005, indigenous transmission of wild-type poliovirus types 1 and 3 had been eliminated from all but four countries: Afghanistan, India, Nigeria, and Pakistan. Wild-type poliovirus type 2 transmission has been globally interrupted. Despite major eradication efforts, outbreaks continue to occur after importation of wild-type virus into previously polio-free countries.
Risk factors for poliovirus infection include overcrowding and poor sanitation, both of which facilitate fecal–oral transmission. Factors associated with increased risk of paralytic disease include B-cell immunodeficiency, strenuous exercise during the early phase of illness, intramuscular injections into affected limbs, and recent tonsillectomy.
Two vaccines are available for prevention: the inactivated poliomyelitis vaccine (IPV) and the live attenuated oral poliomyelitis vaccine (OPV). IPV is administered parenterally and contains all three poliovirus serotypes. It produces excellent systemic immunity, with nearly 100% seroconversion after the third dose, but induces limited intestinal immunity, allowing asymptomatic infection and viral shedding. OPV, used mainly in developing countries, is inexpensive and easy to administer. It induces strong intestinal immunity and enhances herd immunity because vaccinated individuals shed attenuated virus in stool. However, OPV carries a rare risk of vaccine-derived paralytic poliomyelitis, especially in immunocompromised individuals. For this reason, all-IPV schedules are now recommended in the United States and Europe. The routine childhood IPV schedule includes four doses administered at 2 months, 4 months, 6–18 months, and 4–6 years of age.
Humans are the only known reservoir for poliovirus. In developing countries, the fecal–oral route is the principal mode of transmission, while respiratory droplet spread is relatively more important in developed countries. After entering the body, the virus initially infects intestinal epithelial cells and replicates within local lymphatic tissue, causing minor viremia. Infection may terminate at this stage or progress to major viremia involving reticuloendothelial tissues. Central nervous system invasion occurs by retrograde axonal transport from muscle to nerve and spinal cord. Poliovirus preferentially destroys anterior horn cells and motor nuclei within the spinal cord, pons, and medulla, leading to flaccid paralysis affecting the axial muscles, limbs, cranial nerves, or brainstem.
Poliovirus belongs to the family Picornaviridae and genus Enterovirus. Three serotypes exist: types 1, 2, and 3. Infection with one serotype confers immunity only to that serotype, with little cross-protection against the others. Prior to widespread vaccination, serotype 1 caused most paralytic cases.
The incubation period from exposure to the onset of minor illness is approximately 9–12 days, while paralysis generally develops after 11–17 days. Approximately 95% of infections are asymptomatic and detectable only by serology or viral isolation. Abortive poliomyelitis, also known as minor illness, occurs in 4–8% of infected individuals and presents as a nonspecific upper respiratory tract infection with sore throat, low-grade fever, abdominal pain, and diarrhea. Recovery is rapid and complete.
Nonparalytic poliomyelitis occurs in about 1% of infections and is characterized by signs of aseptic meningitis, including neck and back stiffness and pain, following a nonspecific febrile illness. Symptoms usually resolve within 2–10 days.
Spinal paralytic poliomyelitis represents the major form of disease and occurs in approximately 0.1% of infections. Patients develop localized muscle pain and fasciculations several days after the minor illness stage. Fever returns, followed by the rapid onset of asymmetric flaccid paralysis, predominantly involving proximal muscles. Lower extremities are more commonly affected than upper extremities. Sensory loss is typically absent, but deep tendon reflexes are lost. Severe cases may progress to quadriplegia and bulbar involvement.
Bulbar paralytic poliomyelitis involves cranial nerve nuclei, particularly cranial nerves IX and X, leading to dysphagia, nasal speech, and respiratory compromise. Bulbar involvement occurs in 5–35% of paralytic cases and may progress rapidly over several days or even hours. Mixed spinal and bulbar involvement is common. A rare form, polioencephalitis, occurs primarily in children and may present with seizures.
Laboratory evaluation commonly demonstrates cerebrospinal fluid pleocytosis similar to other causes of aseptic meningitis. Poliovirus can be isolated from pharyngeal secretions during the first week of illness and from stool specimens for several weeks. Isolation from cerebrospinal fluid is uncommon. Serologic testing with acute and convalescent sera can confirm infection through neutralizing antibody responses against all three serotypes. Molecular genotyping is important in distinguishing wild-type from vaccine-derived strains.
Neuroimaging studies such as CT or MRI are mainly used to exclude alternative causes of paralysis. MRI may reveal T2-weighted hyperintensities involving the bilateral anterior horn cells. Pathological examination demonstrates neuronal destruction and inflammatory lesions affecting the gray matter of the anterior horns and motor nuclei of the brainstem.
The differential diagnosis includes other enteroviral infections, botulism, West Nile virus infection, transverse myelitis, epidural spinal lesions, tick paralysis, Guillain-Barré syndrome, neuropathies, and stroke. Guillain-Barré syndrome is distinguished by its symmetric ascending paralysis.
There is no specific antiviral therapy for poliomyelitis. Management is primarily supportive. During the acute phase, hospitalization is required for monitoring and supportive care. Strict bed rest is essential to minimize progression of paralysis. Positive pressure ventilation may be necessary when respiratory muscle weakness causes reduced vital capacity. Physical therapy should begin promptly once progression of paralysis has stopped in order to preserve muscle function and prevent contractures. Patients should consume a diet rich in fiber because constipation is common.
The prognosis varies according to disease severity. Bulbar poliomyelitis carries the highest mortality rate, approaching 60%. Approximately two-thirds of patients with paralytic disease are left with some degree of permanent weakness. Complete recovery is uncommon in patients with severe paralysis. Survivors of bulbar paralysis often show substantial improvement within 10 days, and long-term outcome can usually be estimated after one month.
Complications of paralytic poliomyelitis include respiratory failure, gastric dilatation, and paralytic ileus. Years after recovery, some patients develop post-poliomyelitis syndrome, characterized by gradual onset of muscle weakness, pain, fatigue, and muscle atrophy affecting previously involved muscles. This syndrome typically appears 25–35 years after the initial infection.
- Published on
Infectious Disease and Microbiology – Pneumonia
Pneumonia is defined as inflammation of the pulmonary parenchyma caused by an infectious agent. Pneumonia can be categorized according to the clinical setting in which it occurs. These categories include community-acquired pneumonia (CAP), which may be typical or atypical; pneumonia occurring in nursing-home residents; nosocomial pneumonia, including hospital-acquired and ventilator-associated pneumonia; pneumonia in immunocompromised hosts; and aspiration pneumonia.
Pneumonia is a major cause of morbidity and mortality worldwide. Approximately 4 million patients develop pneumonia annually in the United States. Community-acquired pneumonia affects about 12 per 1,000 inhabitants each year, with the highest incidence occurring at the extremes of age. Nosocomial pneumonia develops in approximately 0.5–1.5% of hospitalized patients and is particularly common among mechanically ventilated patients, especially those ventilated for prolonged periods. CAP is more common in children and adults older than 60 years.
Several important risk factors predispose individuals to pneumonia. These include alcoholism, aspiration, endotracheal intubation, immunosuppression, age greater than 65 years, hospitalization or nursing-home residence, particularly ICU stay, and underlying pulmonary diseases such as COPD and cystic fibrosis. Preventive measures include influenza and pneumococcal vaccination and minimizing the duration of endotracheal intubation whenever possible.
The pathophysiology of pneumonia involves activation of the host inflammatory response. Inflammatory mediators and chemokines released by macrophages and recruited neutrophils increase alveolar-capillary permeability, leading to alveolar filling with fluid and inflammatory cells. This results in infiltrates, rales, hemoptysis, hypoxemia, decreased lung compliance, and dyspnea. Increased respiratory drive, airway secretions, and infection-related bronchospasm further contribute to respiratory symptoms.
The etiology of pneumonia varies depending on the clinical setting. In community-acquired pneumonia, Streptococcus pneumoniae remains the most common pathogen. Other important organisms include Mycoplasma pneumoniae, Haemophilus influenzae, Chlamydia pneumoniae, and Staphylococcus aureus, particularly following influenza infection. Community-acquired MRSA strains may cause necrotizing or cavitary pneumonia. Viral pathogens such as hantaviruses, metapneumoviruses, and coronaviruses including SARS are also implicated. Polymicrobial infections are common, and Coxiella burnetii is an important atypical pathogen.
Nosocomial pneumonia is usually caused by gram-negative bacilli such as multidrug-resistant Pseudomonas, Klebsiella, Acinetobacter, and Xanthomonas species. MRSA is also common. Anaerobic bacteria and Legionella species may occasionally be involved, particularly in outbreaks related to contaminated water supplies.
In immunocompromised hosts, the responsible pathogens depend on the nature of the immune defect. Patients with humoral immune deficiencies are susceptible to S. pneumoniae, H. influenzae, S. aureus, and Neisseria species. Granulocyte dysfunction predisposes to gram-negative bacilli and Aspergillus infections. Cellular immune deficiencies increase susceptibility to fungal infections such as Pneumocystis jiroveci, Candida, and Cryptococcus; parasitic infections such as Toxoplasma and Strongyloides; mycobacterial infections; and viral infections including CMV and herpesviruses.
Patients with community-acquired pneumonia often report a recent upper respiratory tract infection. Symptoms commonly include fever, cough, sputum production, pleuritic chest pain, dyspnea, chills, sweats, fatigue, headache, myalgias, and arthralgias. Elderly patients may present atypically with confusion or altered mental status. Nosocomial pneumonia should be suspected in hospitalized patients after more than 48 hours of admission.
Physical examination commonly reveals tachypnea and tachycardia. Tactile fremitus may be increased or decreased. Percussion may demonstrate dullness due to consolidation or pleural fluid. Crackles, bronchial breath sounds, and pleural friction rubs may be present. Severe disease may manifest with hypotension or evidence of organ failure.
Initial laboratory evaluation includes complete blood count, pulse oximetry or arterial blood gas measurements, inflammatory markers such as C-reactive protein, and microbiologic cultures obtained from uncontaminated respiratory specimens. Chest radiography is the primary imaging study. If the initial chest radiograph is negative despite strong clinical suspicion, repeat imaging or chest CT may be necessary. Pneumatoceles suggest S. aureus infection, while upper-lobe cavitary lesions raise suspicion for tuberculosis. CT scanning may help identify post-obstructive pneumonia due to tumors or foreign bodies.
Additional diagnostic procedures may be required in severely ill or diagnostically challenging cases. These include bronchoscopy with bronchoalveolar lavage, transbronchial biopsy, lung biopsy, PCR testing, urinary antigen testing for S. pneumoniae and Legionella, and quantitative cultures. Concurrent endocarditis or meningitis should be excluded when clinically suspected.
The differential diagnosis includes infectious conditions such as bronchitis, empyema, lung abscess, and acute exacerbations of chronic bronchitis, as well as noninfectious conditions such as congestive heart failure, pulmonary embolism, lung cancer, and lymphoma.
Empiric antimicrobial therapy depends on the severity and setting of pneumonia. Outpatients with community-acquired pneumonia who are previously healthy and have not received recent antibiotics may be treated with azithromycin, clarithromycin, or doxycycline. Patients with comorbidities or recent antibiotic exposure should receive either a respiratory fluoroquinolone or a beta-lactam combined with a macrolide. Hospitalized non-ICU patients are generally treated with a respiratory fluoroquinolone or a beta-lactam plus macrolide. ICU patients require broader therapy with a beta-lactam plus azithromycin or a fluoroquinolone. If Pseudomonas is suspected, antipseudomonal agents are required, and linezolid should be added when CA-MRSA is suspected.
Treatment duration for CAP is generally at least 5 days, although many patients require 7–10 days of therapy. Longer treatment courses are necessary for infections due to Legionella, Coxiella burnetii, or S. aureus. Nosocomial pneumonia without MDR risk factors may be treated with ceftriaxone, respiratory fluoroquinolones, ampicillin-sulbactam, or ertapenem. Patients at risk for multidrug-resistant organisms require broad-spectrum antipseudomonal beta-lactams combined with aminoglycosides or fluoroquinolones and MRSA coverage with vancomycin or linezolid.
Supportive management includes adequate hydration, oxygen therapy, and assisted ventilation when necessary. Early administration of empiric antibiotics is critical and should ideally occur within 4 hours of hospital arrival. Severity assessment tools such as CURB-65 and the Pneumonia Severity Index help determine the need for hospitalization.
Patients should be monitored closely for oxygen saturation and clinical response. Discharge is appropriate once the patient is clinically improved, afebrile for at least 72 hours, hemodynamically stable, and able to tolerate oral antibiotics.
Radiographic abnormalities may take 4–12 weeks to resolve. Persistent or recurrent pneumonia should prompt evaluation for underlying malignancy or structural lung disease. Prognosis is generally excellent in outpatients with CAP, with mortality rates below 1%. Mortality rises to approximately 10% among hospitalized patients and is significantly higher in ventilator-associated pneumonia.
Complications include treatment failure due to resistant organisms, inadequate therapy, or noninfectious mimics; metastatic infection; complicated pleural effusions; and lung abscess formation.
Pneumonia is defined as inflammation of the pulmonary parenchyma caused by an infectious agent. Pneumonia can be categorized according to the clinical setting in which it occurs. These categories include community-acquired pneumonia (CAP), which may be typical or atypical; pneumonia occurring in nursing-home residents; nosocomial pneumonia, including hospital-acquired and ventilator-associated pneumonia; pneumonia in immunocompromised hosts; and aspiration pneumonia.
Pneumonia is a major cause of morbidity and mortality worldwide. Approximately 4 million patients develop pneumonia annually in the United States. Community-acquired pneumonia affects about 12 per 1,000 inhabitants each year, with the highest incidence occurring at the extremes of age. Nosocomial pneumonia develops in approximately 0.5–1.5% of hospitalized patients and is particularly common among mechanically ventilated patients, especially those ventilated for prolonged periods. CAP is more common in children and adults older than 60 years.
Several important risk factors predispose individuals to pneumonia. These include alcoholism, aspiration, endotracheal intubation, immunosuppression, age greater than 65 years, hospitalization or nursing-home residence, particularly ICU stay, and underlying pulmonary diseases such as COPD and cystic fibrosis. Preventive measures include influenza and pneumococcal vaccination and minimizing the duration of endotracheal intubation whenever possible.
The pathophysiology of pneumonia involves activation of the host inflammatory response. Inflammatory mediators and chemokines released by macrophages and recruited neutrophils increase alveolar-capillary permeability, leading to alveolar filling with fluid and inflammatory cells. This results in infiltrates, rales, hemoptysis, hypoxemia, decreased lung compliance, and dyspnea. Increased respiratory drive, airway secretions, and infection-related bronchospasm further contribute to respiratory symptoms.
The etiology of pneumonia varies depending on the clinical setting. In community-acquired pneumonia, Streptococcus pneumoniae remains the most common pathogen. Other important organisms include Mycoplasma pneumoniae, Haemophilus influenzae, Chlamydia pneumoniae, and Staphylococcus aureus, particularly following influenza infection. Community-acquired MRSA strains may cause necrotizing or cavitary pneumonia. Viral pathogens such as hantaviruses, metapneumoviruses, and coronaviruses including SARS are also implicated. Polymicrobial infections are common, and Coxiella burnetii is an important atypical pathogen.
Nosocomial pneumonia is usually caused by gram-negative bacilli such as multidrug-resistant Pseudomonas, Klebsiella, Acinetobacter, and Xanthomonas species. MRSA is also common. Anaerobic bacteria and Legionella species may occasionally be involved, particularly in outbreaks related to contaminated water supplies.
In immunocompromised hosts, the responsible pathogens depend on the nature of the immune defect. Patients with humoral immune deficiencies are susceptible to S. pneumoniae, H. influenzae, S. aureus, and Neisseria species. Granulocyte dysfunction predisposes to gram-negative bacilli and Aspergillus infections. Cellular immune deficiencies increase susceptibility to fungal infections such as Pneumocystis jiroveci, Candida, and Cryptococcus; parasitic infections such as Toxoplasma and Strongyloides; mycobacterial infections; and viral infections including CMV and herpesviruses.
Patients with community-acquired pneumonia often report a recent upper respiratory tract infection. Symptoms commonly include fever, cough, sputum production, pleuritic chest pain, dyspnea, chills, sweats, fatigue, headache, myalgias, and arthralgias. Elderly patients may present atypically with confusion or altered mental status. Nosocomial pneumonia should be suspected in hospitalized patients after more than 48 hours of admission.
Physical examination commonly reveals tachypnea and tachycardia. Tactile fremitus may be increased or decreased. Percussion may demonstrate dullness due to consolidation or pleural fluid. Crackles, bronchial breath sounds, and pleural friction rubs may be present. Severe disease may manifest with hypotension or evidence of organ failure.
Initial laboratory evaluation includes complete blood count, pulse oximetry or arterial blood gas measurements, inflammatory markers such as C-reactive protein, and microbiologic cultures obtained from uncontaminated respiratory specimens. Chest radiography is the primary imaging study. If the initial chest radiograph is negative despite strong clinical suspicion, repeat imaging or chest CT may be necessary. Pneumatoceles suggest S. aureus infection, while upper-lobe cavitary lesions raise suspicion for tuberculosis. CT scanning may help identify post-obstructive pneumonia due to tumors or foreign bodies.
Additional diagnostic procedures may be required in severely ill or diagnostically challenging cases. These include bronchoscopy with bronchoalveolar lavage, transbronchial biopsy, lung biopsy, PCR testing, urinary antigen testing for S. pneumoniae and Legionella, and quantitative cultures. Concurrent endocarditis or meningitis should be excluded when clinically suspected.
The differential diagnosis includes infectious conditions such as bronchitis, empyema, lung abscess, and acute exacerbations of chronic bronchitis, as well as noninfectious conditions such as congestive heart failure, pulmonary embolism, lung cancer, and lymphoma.
Empiric antimicrobial therapy depends on the severity and setting of pneumonia. Outpatients with community-acquired pneumonia who are previously healthy and have not received recent antibiotics may be treated with azithromycin, clarithromycin, or doxycycline. Patients with comorbidities or recent antibiotic exposure should receive either a respiratory fluoroquinolone or a beta-lactam combined with a macrolide. Hospitalized non-ICU patients are generally treated with a respiratory fluoroquinolone or a beta-lactam plus macrolide. ICU patients require broader therapy with a beta-lactam plus azithromycin or a fluoroquinolone. If Pseudomonas is suspected, antipseudomonal agents are required, and linezolid should be added when CA-MRSA is suspected.
Treatment duration for CAP is generally at least 5 days, although many patients require 7–10 days of therapy. Longer treatment courses are necessary for infections due to Legionella, Coxiella burnetii, or S. aureus. Nosocomial pneumonia without MDR risk factors may be treated with ceftriaxone, respiratory fluoroquinolones, ampicillin-sulbactam, or ertapenem. Patients at risk for multidrug-resistant organisms require broad-spectrum antipseudomonal beta-lactams combined with aminoglycosides or fluoroquinolones and MRSA coverage with vancomycin or linezolid.
Supportive management includes adequate hydration, oxygen therapy, and assisted ventilation when necessary. Early administration of empiric antibiotics is critical and should ideally occur within 4 hours of hospital arrival. Severity assessment tools such as CURB-65 and the Pneumonia Severity Index help determine the need for hospitalization.
Patients should be monitored closely for oxygen saturation and clinical response. Discharge is appropriate once the patient is clinically improved, afebrile for at least 72 hours, hemodynamically stable, and able to tolerate oral antibiotics.
Radiographic abnormalities may take 4–12 weeks to resolve. Persistent or recurrent pneumonia should prompt evaluation for underlying malignancy or structural lung disease. Prognosis is generally excellent in outpatients with CAP, with mortality rates below 1%. Mortality rises to approximately 10% among hospitalized patients and is significantly higher in ventilator-associated pneumonia.
Complications include treatment failure due to resistant organisms, inadequate therapy, or noninfectious mimics; metastatic infection; complicated pleural effusions; and lung abscess formation.
- Published on
Infectious Disease and Microbiology -Pneumocystis jiroveci (Carinii) Infection
Pneumocystis jiroveci is an opportunistic fungal pathogen whose natural habitat is the lung. It is an important cause of pneumonia in immunocompromised patients, especially individuals with HIV/AIDS. The disease is commonly referred to as Pneumocystis pneumonia (PCP). Although formerly known as Pneumocystis carinii, the organism infecting humans is now correctly termed Pneumocystis jiroveci. Despite advances in prophylaxis and antiretroviral therapy, PCP remains one of the most common opportunistic infections in HIV-infected patients.
The incidence of PCP has decreased substantially because of routine prophylaxis and improved HIV management. However, it still occurs frequently among patients with advanced immunosuppression. PCP has also been reported in patients receiving immunomodulatory therapies such as infliximab and etanercept. Extrapulmonary disease is uncommon, occurring in fewer than 3% of cases. Internationally, the reported incidence is considered low, although this is likely due to underdiagnosis. PCP is particularly important in HIV-infected infants, among whom it is responsible for a large proportion of pneumonia cases.
Major risk factors include HIV/AIDS with CD4 counts below 200/mm³, malignancy, long-term corticosteroid or immunosuppressive therapy, primary immunodeficiency syndromes, tobacco use, and severe malnutrition. Patients with organ transplants, hematologic malignancies, and severe combined immunodeficiency are also at increased risk. Because of these risks, prophylaxis is recommended for high-risk HIV-infected individuals and certain other immunocompromised populations.
Primary prophylaxis is indicated in HIV-infected patients with CD4 counts below 200/mm³ or in those with oropharyngeal candidiasis regardless of CD4 count. The preferred prophylactic regimen is one double-strength tablet of trimethoprim-sulfamethoxazole daily. Alternative regimens include reduced-dose TMP-SMX, dapsone-based regimens, nebulized pentamidine, or pyrimethamine combinations. Secondary prophylaxis is recommended for all patients recovering from PCP until immune reconstitution occurs.
Infection with P. jiroveci usually occurs early in childhood, and many healthy individuals harbor the organism in their lungs without disease. In immunocompromised hosts, defective cellular immunity—especially impaired CD4 T-cell function—prevents effective clearance of the organism. Activated macrophages become unable to eliminate the fungus, resulting in increased alveolar-capillary permeability and impaired gas exchange. This process produces hypoxemia, respiratory alkalosis, and diffuse interstitial pneumonia.
Patients usually present with nonspecific symptoms such as progressive exertional dyspnea, fever, dry cough, chest discomfort, chills, and weight loss. In HIV-infected individuals, the illness often develops gradually over days to weeks, whereas in non-HIV immunocompromised patients the disease may progress rapidly and severely. Hemoptysis is uncommon but may occur.
On physical examination, patients commonly have tachypnea, fever, and tachycardia. Pulmonary examination may be surprisingly normal in up to half of patients despite significant hypoxemia. Children with severe disease may exhibit cyanosis, nasal flaring, and intercostal retractions. Rare extrapulmonary manifestations can involve the central nervous system, thyroid, gastrointestinal tract, lymph nodes, eyes, and bone marrow.
Laboratory findings are nonspecific. Elevated lactate dehydrogenase (LDH) levels are common but not diagnostic. Serum β-D-glucan levels are frequently elevated. Arterial blood gas analysis typically demonstrates hypoxemia, respiratory alkalosis, and an increased alveolar–arterial oxygen gradient. Disease severity is often classified according to the degree of alveolar–arterial gradient elevation.
Chest radiography classically demonstrates bilateral diffuse perihilar infiltrates, although early disease may show a normal chest x-ray. Chest CT scanning is more sensitive and commonly reveals diffuse bilateral ground-glass opacities. Patients receiving aerosolized pentamidine prophylaxis may show upper-lobe infiltrates and are at increased risk for pneumothorax.
Definitive diagnosis requires identification of the organism in respiratory specimens. Fiberoptic bronchoscopy with bronchoalveolar lavage remains the diagnostic standard. Induced sputum may be used but has variable sensitivity. Histopathologic stains such as methenamine silver, toluidine blue, Giemsa, and immunofluorescent stains are used to identify cysts and trophozoites. More invasive procedures such as transbronchial biopsy or open-lung biopsy are reserved for difficult cases.
The differential diagnosis includes other causes of diffuse pneumonia and respiratory failure, including tuberculosis, cytomegalovirus pneumonia, viral pneumonias, Legionella infection, fungal pneumonias, pulmonary embolism, ARDS, congestive heart failure, and pulmonary involvement by Kaposi sarcoma or lymphoma.
Trimethoprim-sulfamethoxazole (TMP-SMX) is the treatment of choice for PCP. The recommended dose is 15–20 mg/kg/day of the trimethoprim component, administered orally or intravenously in divided doses. Treatment duration is 21 days in HIV-infected patients and 14 days in non-HIV patients. Clinical improvement usually occurs within several days, although clinicians should wait at least 4–8 days before concluding treatment failure.
Adjunctive corticosteroids significantly improve survival in patients with moderate to severe disease, particularly in HIV-associated PCP. Steroids are indicated in patients with a PaO₂ below 70 mm Hg or an alveolar–arterial gradient greater than or equal to 35 mm Hg. Prednisone is typically administered in tapering doses over 21 days and should be started within 72 hours of initiating antimicrobial therapy.
Alternative therapies are used when TMP-SMX cannot be tolerated or when treatment failure occurs. Intravenous pentamidine is an effective alternative but may cause significant toxicities including hypotension, arrhythmias, pancreatitis, dysglycemia, renal dysfunction, electrolyte abnormalities, and neutropenia. Other options include clindamycin plus primaquine, atovaquone, or trimethoprim plus dapsone. Primaquine should be avoided in patients with glucose-6-phosphate dehydrogenase deficiency.
Patients require close monitoring for clinical response, oxygenation status, and medication-related adverse effects. Complications include progressive respiratory failure, pneumothorax, concurrent pulmonary infections, and death. Mortality rates are approximately 10–20% among HIV-infected patients but may reach 30–50% in non-HIV immunocompromised individuals, largely due to delayed diagnosis and treatment. Early recognition and prompt therapy remain essential for improving outcomes.
Pneumocystis jiroveci is an opportunistic fungal pathogen whose natural habitat is the lung. It is an important cause of pneumonia in immunocompromised patients, especially individuals with HIV/AIDS. The disease is commonly referred to as Pneumocystis pneumonia (PCP). Although formerly known as Pneumocystis carinii, the organism infecting humans is now correctly termed Pneumocystis jiroveci. Despite advances in prophylaxis and antiretroviral therapy, PCP remains one of the most common opportunistic infections in HIV-infected patients.
The incidence of PCP has decreased substantially because of routine prophylaxis and improved HIV management. However, it still occurs frequently among patients with advanced immunosuppression. PCP has also been reported in patients receiving immunomodulatory therapies such as infliximab and etanercept. Extrapulmonary disease is uncommon, occurring in fewer than 3% of cases. Internationally, the reported incidence is considered low, although this is likely due to underdiagnosis. PCP is particularly important in HIV-infected infants, among whom it is responsible for a large proportion of pneumonia cases.
Major risk factors include HIV/AIDS with CD4 counts below 200/mm³, malignancy, long-term corticosteroid or immunosuppressive therapy, primary immunodeficiency syndromes, tobacco use, and severe malnutrition. Patients with organ transplants, hematologic malignancies, and severe combined immunodeficiency are also at increased risk. Because of these risks, prophylaxis is recommended for high-risk HIV-infected individuals and certain other immunocompromised populations.
Primary prophylaxis is indicated in HIV-infected patients with CD4 counts below 200/mm³ or in those with oropharyngeal candidiasis regardless of CD4 count. The preferred prophylactic regimen is one double-strength tablet of trimethoprim-sulfamethoxazole daily. Alternative regimens include reduced-dose TMP-SMX, dapsone-based regimens, nebulized pentamidine, or pyrimethamine combinations. Secondary prophylaxis is recommended for all patients recovering from PCP until immune reconstitution occurs.
Infection with P. jiroveci usually occurs early in childhood, and many healthy individuals harbor the organism in their lungs without disease. In immunocompromised hosts, defective cellular immunity—especially impaired CD4 T-cell function—prevents effective clearance of the organism. Activated macrophages become unable to eliminate the fungus, resulting in increased alveolar-capillary permeability and impaired gas exchange. This process produces hypoxemia, respiratory alkalosis, and diffuse interstitial pneumonia.
Patients usually present with nonspecific symptoms such as progressive exertional dyspnea, fever, dry cough, chest discomfort, chills, and weight loss. In HIV-infected individuals, the illness often develops gradually over days to weeks, whereas in non-HIV immunocompromised patients the disease may progress rapidly and severely. Hemoptysis is uncommon but may occur.
On physical examination, patients commonly have tachypnea, fever, and tachycardia. Pulmonary examination may be surprisingly normal in up to half of patients despite significant hypoxemia. Children with severe disease may exhibit cyanosis, nasal flaring, and intercostal retractions. Rare extrapulmonary manifestations can involve the central nervous system, thyroid, gastrointestinal tract, lymph nodes, eyes, and bone marrow.
Laboratory findings are nonspecific. Elevated lactate dehydrogenase (LDH) levels are common but not diagnostic. Serum β-D-glucan levels are frequently elevated. Arterial blood gas analysis typically demonstrates hypoxemia, respiratory alkalosis, and an increased alveolar–arterial oxygen gradient. Disease severity is often classified according to the degree of alveolar–arterial gradient elevation.
Chest radiography classically demonstrates bilateral diffuse perihilar infiltrates, although early disease may show a normal chest x-ray. Chest CT scanning is more sensitive and commonly reveals diffuse bilateral ground-glass opacities. Patients receiving aerosolized pentamidine prophylaxis may show upper-lobe infiltrates and are at increased risk for pneumothorax.
Definitive diagnosis requires identification of the organism in respiratory specimens. Fiberoptic bronchoscopy with bronchoalveolar lavage remains the diagnostic standard. Induced sputum may be used but has variable sensitivity. Histopathologic stains such as methenamine silver, toluidine blue, Giemsa, and immunofluorescent stains are used to identify cysts and trophozoites. More invasive procedures such as transbronchial biopsy or open-lung biopsy are reserved for difficult cases.
The differential diagnosis includes other causes of diffuse pneumonia and respiratory failure, including tuberculosis, cytomegalovirus pneumonia, viral pneumonias, Legionella infection, fungal pneumonias, pulmonary embolism, ARDS, congestive heart failure, and pulmonary involvement by Kaposi sarcoma or lymphoma.
Trimethoprim-sulfamethoxazole (TMP-SMX) is the treatment of choice for PCP. The recommended dose is 15–20 mg/kg/day of the trimethoprim component, administered orally or intravenously in divided doses. Treatment duration is 21 days in HIV-infected patients and 14 days in non-HIV patients. Clinical improvement usually occurs within several days, although clinicians should wait at least 4–8 days before concluding treatment failure.
Adjunctive corticosteroids significantly improve survival in patients with moderate to severe disease, particularly in HIV-associated PCP. Steroids are indicated in patients with a PaO₂ below 70 mm Hg or an alveolar–arterial gradient greater than or equal to 35 mm Hg. Prednisone is typically administered in tapering doses over 21 days and should be started within 72 hours of initiating antimicrobial therapy.
Alternative therapies are used when TMP-SMX cannot be tolerated or when treatment failure occurs. Intravenous pentamidine is an effective alternative but may cause significant toxicities including hypotension, arrhythmias, pancreatitis, dysglycemia, renal dysfunction, electrolyte abnormalities, and neutropenia. Other options include clindamycin plus primaquine, atovaquone, or trimethoprim plus dapsone. Primaquine should be avoided in patients with glucose-6-phosphate dehydrogenase deficiency.
Patients require close monitoring for clinical response, oxygenation status, and medication-related adverse effects. Complications include progressive respiratory failure, pneumothorax, concurrent pulmonary infections, and death. Mortality rates are approximately 10–20% among HIV-infected patients but may reach 30–50% in non-HIV immunocompromised individuals, largely due to delayed diagnosis and treatment. Early recognition and prompt therapy remain essential for improving outcomes.
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Infectious disease and microbiology – Plague
Plague is a severe zoonotic infection caused by Yersinia pestis, a gram-negative aerobic coccobacillus belonging to the Enterobacteriaceae family. Historically, plague caused the devastating “Black Death” pandemics of the Middle Ages. Clinically, the disease may present as bubonic, septicemic, pneumonic, meningeal, or pharyngeal plague.
Plague remains endemic in several regions of the world, especially in parts of Africa, Asia, and the Americas. Between 1998 and 2003, more than 38,000 cases and nearly 3,000 deaths were reported globally. In the United States, most cases occur in the southwestern states, particularly New Mexico, Arizona, and Colorado.
Major risk factors include residence or travel in endemic areas, poor rodent control, exposure to rodents or rodent predators, occupational exposure among veterinarians and laboratory workers, close contact with infected animals, and inadequate flea control in domestic animals.
The disease is maintained in nature through an enzootic cycle involving rodents and fleas. Humans are accidental hosts and do not contribute significantly to maintaining transmission. Infection occurs through:
Clinical Forms
Bubonic plague
The most common presentation.
Symptoms
Septicemic plague
May occur primarily or as progression from bubonic disease.
Features
Pneumonic plague
The most dangerous and contagious form.
Symptoms
Meningeal plague
Rare complication due to CNS seeding during bacteremia.
Features
Diagnosis
Laboratory abnormalities may include:
Special culture media include:
Chest radiography in pneumonic plague may show:
Treatment
First-line therapy
Aminoglycosides
Alternative agents
Supportive Care
Management may also require:
Infection Control
Pneumonic plague
Requires:
Standard precautions are usually sufficient.
Healthcare and laboratory personnel should be informed immediately if plague is suspected because Y. pestis is considered a potential bioterrorism agent owing to its high virulence and aerosol transmissibility.
Prognosis and Complications
Untreated plague has mortality rates approaching 50%, while untreated pneumonic plague is almost universally fatal.
Complications include:
Plague is a severe zoonotic infection caused by Yersinia pestis, a gram-negative aerobic coccobacillus belonging to the Enterobacteriaceae family. Historically, plague caused the devastating “Black Death” pandemics of the Middle Ages. Clinically, the disease may present as bubonic, septicemic, pneumonic, meningeal, or pharyngeal plague.
Plague remains endemic in several regions of the world, especially in parts of Africa, Asia, and the Americas. Between 1998 and 2003, more than 38,000 cases and nearly 3,000 deaths were reported globally. In the United States, most cases occur in the southwestern states, particularly New Mexico, Arizona, and Colorado.
Major risk factors include residence or travel in endemic areas, poor rodent control, exposure to rodents or rodent predators, occupational exposure among veterinarians and laboratory workers, close contact with infected animals, and inadequate flea control in domestic animals.
The disease is maintained in nature through an enzootic cycle involving rodents and fleas. Humans are accidental hosts and do not contribute significantly to maintaining transmission. Infection occurs through:
- Bite of an infected flea
- Direct contact with infected animals or carcasses
- Inhalation of respiratory droplets from pneumonic plague patients or infected animals
Clinical Forms
Bubonic plague
The most common presentation.
Symptoms
- Sudden fever and chills
- Headache and weakness
- Painful swollen lymph nodes (“buboes”) appearing within 24 hours
- Large, tender, erythematous lymph nodes
- Usually inguinal or femoral nodes
- Buboes may ulcerate
- Flea-bite papules or pustules may be present
Septicemic plague
May occur primarily or as progression from bubonic disease.
Features
- Severe sepsis and toxic appearance
- Hypotension
- Gastrointestinal symptoms
- Disseminated intravascular coagulation
- Acral gangrene (“black death”)
- Buboes may be absent
Pneumonic plague
The most dangerous and contagious form.
Symptoms
- Rapidly progressive pneumonia
- Productive cough with bloody sputum
- Pleuritic chest pain
- Severe respiratory distress and hypoxia
Meningeal plague
Rare complication due to CNS seeding during bacteremia.
Features
- Fever
- Headache
- Neck stiffness
Diagnosis
Laboratory abnormalities may include:
- Leukocytosis
- Thrombocytopenia
- Elevated liver enzymes
- Elevated creatinine and BUN
- Disseminated intravascular coagulation in severe disease
- Bubo aspirates
- Sputum
- Throat swabs
- CSF
- Skin swabs
Special culture media include:
- MacConkey agar
- Chocolate agar
- Sheep blood agar
- Brain-heart infusion broth
Chest radiography in pneumonic plague may show:
- Lobar or patchy infiltrates
- Cavitation
- Pleural effusions
- ARDS-like diffuse opacities
Treatment
First-line therapy
Aminoglycosides
- Streptomycin 30 mg/kg/day IM in 2 divided doses
- Gentamicin 2.5 mg/kg IM every 12 hours
Alternative agents
- Doxycycline
- Tetracycline
- Chloramphenicol
- TMP-SMX
Supportive Care
Management may also require:
- Intravenous fluids
- Analgesics and antipyretics
- Intensive care support for septic shock or respiratory failure
Infection Control
Pneumonic plague
Requires:
- Respiratory droplet isolation
- Hospital admission
- Immediate antimicrobial treatment
Standard precautions are usually sufficient.
Healthcare and laboratory personnel should be informed immediately if plague is suspected because Y. pestis is considered a potential bioterrorism agent owing to its high virulence and aerosol transmissibility.
Prognosis and Complications
Untreated plague has mortality rates approaching 50%, while untreated pneumonic plague is almost universally fatal.
Complications include:
- Pneumonia
- Septic shock
- Multiorgan failure
- Respiratory failure
- Disseminated intravascular coagulation
- Secondary bacterial superinfection of buboes
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Infectious disease and microbiology – Pilonidal abscess
A pilonidal abscess is an infection of a pilonidal cyst, usually located in the postanal or sacrococcygeal region within the natal cleft. Pilonidal disease is now considered an acquired condition rather than congenital and ranges from asymptomatic pits to painful abscesses and chronic draining sinuses.
The disease is relatively common, with approximately 70,000 new cases annually in the United States. It occurs most often in young adults between 18 and 30 years of age and is significantly more common in males than females, with a male-to-female ratio of about 3:1. Higher rates are reported in Mediterranean populations, whereas the disease is relatively uncommon in East Asia, Oceania, and sub-Saharan Africa.
Several risk factors contribute to pilonidal disease, including male gender, obesity, excessive body hair, poor hygiene, and a deep natal cleft. Although prevention is difficult, maintaining good perianal hygiene and regular hair removal may reduce recurrence and progression.
The pathogenesis involves the formation of a hair follicle pit in the natal cleft, which enlarges and fills with keratin and debris. Hair penetration into the skin triggers a foreign body inflammatory reaction, leading to infection of the surrounding subcutaneous tissue. Chronic disease may result in sinus tract formation, with the direction of hair insertion influencing the tract pattern.
The exact microbial causes are variable, but infections are usually polymicrobial and involve organisms from the skin flora and bowel flora, including anaerobic bacteria.
Clinically, patients typically present with a painful, tender, warm, fluctuant swelling in the sacrococcygeal area during acute infection. Chronic disease may produce persistent or intermittent drainage from midline pits or sinus tracts, with symptoms waxing and waning over weeks.
Diagnosis is mainly clinical and based on physical examination. Characteristic findings include midline pits in the gluteal cleft, usually located approximately 5 cm above the anus. Acute abscesses, chronic sinus tracts, or minimal inflammation may be present. An anorectal examination is important to exclude other conditions.
The differential diagnosis includes both infectious and noninfectious disorders such as perianal abscess, hidradenitis suppurativa, necrotizing fasciitis, furunculosis, herpes simplex infection, syphilis, tuberculosis, anal fistulas, Crohn disease, coccygodynia, and radiation proctitis.
Management depends on the severity and chronicity of disease. Antibiotics alone have a limited role but may be useful in patients with associated cellulitis, systemic illness, or immunosuppression. When used, therapy should include anaerobic coverage. Meticulous local hygiene and hair removal are recommended as supportive measures.
For minimally symptomatic disease, nonsurgical therapies such as phenol or fibrin glue injection combined with hygiene and hair control may be attempted. However, the mainstay of treatment for most acute or chronic cases is surgical management. Limited excision with an off-midline incision and removal of the sinus pits is often sufficient and allows quicker recovery with acceptable recurrence rates. More extensive recurrent or complicated disease may require wide excision and reconstruction with flattening of the natal cleft, although this approach carries higher morbidity.
The overall prognosis is excellent, though recurrence is relatively common and may necessitate repeat or more extensive surgery. Rare complications include large abscesses leading to sepsis and shock, and in very long-standing untreated disease, the development of carcinoma arising from a chronic pilonidal sinus.
A pilonidal abscess is an infection of a pilonidal cyst, usually located in the postanal or sacrococcygeal region within the natal cleft. Pilonidal disease is now considered an acquired condition rather than congenital and ranges from asymptomatic pits to painful abscesses and chronic draining sinuses.
The disease is relatively common, with approximately 70,000 new cases annually in the United States. It occurs most often in young adults between 18 and 30 years of age and is significantly more common in males than females, with a male-to-female ratio of about 3:1. Higher rates are reported in Mediterranean populations, whereas the disease is relatively uncommon in East Asia, Oceania, and sub-Saharan Africa.
Several risk factors contribute to pilonidal disease, including male gender, obesity, excessive body hair, poor hygiene, and a deep natal cleft. Although prevention is difficult, maintaining good perianal hygiene and regular hair removal may reduce recurrence and progression.
The pathogenesis involves the formation of a hair follicle pit in the natal cleft, which enlarges and fills with keratin and debris. Hair penetration into the skin triggers a foreign body inflammatory reaction, leading to infection of the surrounding subcutaneous tissue. Chronic disease may result in sinus tract formation, with the direction of hair insertion influencing the tract pattern.
The exact microbial causes are variable, but infections are usually polymicrobial and involve organisms from the skin flora and bowel flora, including anaerobic bacteria.
Clinically, patients typically present with a painful, tender, warm, fluctuant swelling in the sacrococcygeal area during acute infection. Chronic disease may produce persistent or intermittent drainage from midline pits or sinus tracts, with symptoms waxing and waning over weeks.
Diagnosis is mainly clinical and based on physical examination. Characteristic findings include midline pits in the gluteal cleft, usually located approximately 5 cm above the anus. Acute abscesses, chronic sinus tracts, or minimal inflammation may be present. An anorectal examination is important to exclude other conditions.
The differential diagnosis includes both infectious and noninfectious disorders such as perianal abscess, hidradenitis suppurativa, necrotizing fasciitis, furunculosis, herpes simplex infection, syphilis, tuberculosis, anal fistulas, Crohn disease, coccygodynia, and radiation proctitis.
Management depends on the severity and chronicity of disease. Antibiotics alone have a limited role but may be useful in patients with associated cellulitis, systemic illness, or immunosuppression. When used, therapy should include anaerobic coverage. Meticulous local hygiene and hair removal are recommended as supportive measures.
For minimally symptomatic disease, nonsurgical therapies such as phenol or fibrin glue injection combined with hygiene and hair control may be attempted. However, the mainstay of treatment for most acute or chronic cases is surgical management. Limited excision with an off-midline incision and removal of the sinus pits is often sufficient and allows quicker recovery with acceptable recurrence rates. More extensive recurrent or complicated disease may require wide excision and reconstruction with flattening of the natal cleft, although this approach carries higher morbidity.
The overall prognosis is excellent, though recurrence is relatively common and may necessitate repeat or more extensive surgery. Rare complications include large abscesses leading to sepsis and shock, and in very long-standing untreated disease, the development of carcinoma arising from a chronic pilonidal sinus.
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Toxicology – Black Widow Spider (Latrodectus) Envenomation
Source
Black widow spiders are found throughout the United States, especially in warmer southern regions. Only female spiders bite humans. They are typically identified by markings on the abdomen—most commonly a red hourglass on the underside. These spiders tend to inhabit dark, undisturbed areas such as woodpiles, garages, and sheds.
Typical Presentation
Patients often present after a painful spider bite followed by progressive muscle pain and systemic symptoms. In children, symptoms may be severe and mimic other acute conditions such as abdominal emergencies.
Clinical Features
The bite initially causes localized pain, followed by redness and sweating at the site. Systemic symptoms may include muscle cramps and fasciculations, severe abdominal pain and rigidity, nausea, vomiting, weakness, headache, dizziness, chest pain, and elevated blood pressure. In some cases, unusual findings such as priapism may occur. Symptoms tend to be more severe in children and older adults.
Mechanism of Action
The venom contains alpha-latrotoxin, a potent neurotoxin that triggers massive release of neurotransmitters by opening presynaptic calcium channels. This results in widespread neuromuscular and autonomic stimulation.
Management
Treatment is primarily supportive, focusing on pain control and symptom management. Muscle relaxants may be used for cramping. Intravenous calcium has been used in some cases, though benefits are variable. Antivenom may be considered in severe cases, particularly in high-risk patients or those with significant systemic symptoms.
Key Points
Source
Black widow spiders are found throughout the United States, especially in warmer southern regions. Only female spiders bite humans. They are typically identified by markings on the abdomen—most commonly a red hourglass on the underside. These spiders tend to inhabit dark, undisturbed areas such as woodpiles, garages, and sheds.
Typical Presentation
Patients often present after a painful spider bite followed by progressive muscle pain and systemic symptoms. In children, symptoms may be severe and mimic other acute conditions such as abdominal emergencies.
Clinical Features
The bite initially causes localized pain, followed by redness and sweating at the site. Systemic symptoms may include muscle cramps and fasciculations, severe abdominal pain and rigidity, nausea, vomiting, weakness, headache, dizziness, chest pain, and elevated blood pressure. In some cases, unusual findings such as priapism may occur. Symptoms tend to be more severe in children and older adults.
Mechanism of Action
The venom contains alpha-latrotoxin, a potent neurotoxin that triggers massive release of neurotransmitters by opening presynaptic calcium channels. This results in widespread neuromuscular and autonomic stimulation.
Management
Treatment is primarily supportive, focusing on pain control and symptom management. Muscle relaxants may be used for cramping. Intravenous calcium has been used in some cases, though benefits are variable. Antivenom may be considered in severe cases, particularly in high-risk patients or those with significant systemic symptoms.
Key Points
- Symptoms may mimic conditions such as acute abdomen or cardiac ischemia.
- Severe complications can include hypertensive crises and respiratory compromise.
- Early recognition and supportive care are essential for good outcomes.
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Infectious disease and microbiology – Orchitis
Orchitis is an inflammatory condition of the testes, most commonly caused by infection. It often occurs alongside epididymitis (epididymo-orchitis), in which case both conditions share similar causative organisms. Unlike many other genitourinary infections, viral causes—especially mumps—play a significant role, particularly in isolated orchitis. Although relatively uncommon compared to other urinary tract infections in men, orchitis is frequently encountered in outpatient settings and is associated with epididymitis in up to 20–40% of cases.
The infection typically develops through either direct spread from the epididymis or hematogenous dissemination in primary testicular infection. Risk factors include urethral catheterization, sexually transmitted infections (STIs), and underlying epididymitis, while prevention focuses on safe sexual practices and vaccination against mumps.
The etiology varies by age and risk profile. In younger men (14–35 years), the most common bacterial causes are Neisseria gonorrhoeae and Chlamydia trachomatis, whereas in older individuals, enteric Gram-negative bacteria such as Escherichia coli, Klebsiella, and Proteus predominate. Viral orchitis is most frequently caused by mumps virus, particularly in post-pubertal males, where it occurs in 20–30% of infections. Less commonly, fungi and rare pathogens such as Brucella or Mycobacterium tuberculosis may be involved.
Clinically, patients present with testicular pain, swelling, and tenderness, often accompanied by fever, nausea, and systemic symptoms. Viral orchitis, especially mumps-related, typically has an abrupt onset, often following parotitis by several days. The condition usually resolves within 1–2 weeks, although residual tenderness may persist. On examination, testicular enlargement with a preserved cremasteric reflex is typical, helping differentiate it from testicular torsion—a critical diagnosis that must always be excluded.
Diagnosis is based on clinical findings supported by laboratory tests and imaging. Urinalysis, urine culture, and testing for STIs (including PCR for Chlamydia and Gonorrhea) are essential. In suspected viral cases, serologic testing or PCR can confirm the diagnosis. Color Doppler ultrasonography is particularly important to rule out testicular torsion, which is the most urgent differential diagnosis.
Management depends on the underlying cause. Bacterial orchitis is treated with appropriate antibiotics, often covering both gonorrhea and chlamydia empirically (e.g., ceftriaxone plus doxycycline). Enteric infections are treated with β-lactam/β-lactamase inhibitors, cephalosporins, or fluoroquinolones. In contrast, viral orchitis has no specific antiviral treatment, and management is supportive, including rest, scrotal elevation, and cold compresses. Surgical intervention may be required in cases of abscess formation or complications.
The prognosis is generally favorable, especially in viral cases like mumps orchitis, which rarely leads to infertility, although testicular atrophy and abnormalities in sperm parameters may occur. Potential complications include testicular infarction, abscess formation, pyocele, and, rarely, infertility, emphasizing the importance of timely diagnosis and appropriate management.
Orchitis is an inflammatory condition of the testes, most commonly caused by infection. It often occurs alongside epididymitis (epididymo-orchitis), in which case both conditions share similar causative organisms. Unlike many other genitourinary infections, viral causes—especially mumps—play a significant role, particularly in isolated orchitis. Although relatively uncommon compared to other urinary tract infections in men, orchitis is frequently encountered in outpatient settings and is associated with epididymitis in up to 20–40% of cases.
The infection typically develops through either direct spread from the epididymis or hematogenous dissemination in primary testicular infection. Risk factors include urethral catheterization, sexually transmitted infections (STIs), and underlying epididymitis, while prevention focuses on safe sexual practices and vaccination against mumps.
The etiology varies by age and risk profile. In younger men (14–35 years), the most common bacterial causes are Neisseria gonorrhoeae and Chlamydia trachomatis, whereas in older individuals, enteric Gram-negative bacteria such as Escherichia coli, Klebsiella, and Proteus predominate. Viral orchitis is most frequently caused by mumps virus, particularly in post-pubertal males, where it occurs in 20–30% of infections. Less commonly, fungi and rare pathogens such as Brucella or Mycobacterium tuberculosis may be involved.
Clinically, patients present with testicular pain, swelling, and tenderness, often accompanied by fever, nausea, and systemic symptoms. Viral orchitis, especially mumps-related, typically has an abrupt onset, often following parotitis by several days. The condition usually resolves within 1–2 weeks, although residual tenderness may persist. On examination, testicular enlargement with a preserved cremasteric reflex is typical, helping differentiate it from testicular torsion—a critical diagnosis that must always be excluded.
Diagnosis is based on clinical findings supported by laboratory tests and imaging. Urinalysis, urine culture, and testing for STIs (including PCR for Chlamydia and Gonorrhea) are essential. In suspected viral cases, serologic testing or PCR can confirm the diagnosis. Color Doppler ultrasonography is particularly important to rule out testicular torsion, which is the most urgent differential diagnosis.
Management depends on the underlying cause. Bacterial orchitis is treated with appropriate antibiotics, often covering both gonorrhea and chlamydia empirically (e.g., ceftriaxone plus doxycycline). Enteric infections are treated with β-lactam/β-lactamase inhibitors, cephalosporins, or fluoroquinolones. In contrast, viral orchitis has no specific antiviral treatment, and management is supportive, including rest, scrotal elevation, and cold compresses. Surgical intervention may be required in cases of abscess formation or complications.
The prognosis is generally favorable, especially in viral cases like mumps orchitis, which rarely leads to infertility, although testicular atrophy and abnormalities in sperm parameters may occur. Potential complications include testicular infarction, abscess formation, pyocele, and, rarely, infertility, emphasizing the importance of timely diagnosis and appropriate management.
