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Infectious Disease And Microbiology – Erythema Nodosum
Erythema nodosum is the most common form of panniculitis, characterized by inflammatory, tender nodules that typically appear on the lower extremities, especially the shins. It represents a reactive process rather than a primary infection and is often associated with a wide range of underlying conditions.
Epidemiologically, erythema nodosum most frequently affects individuals between 18 and 34 years of age and is more common in females. The annual incidence in hospitalized patients has been estimated at 52 cases per million people, with an overall prevalence of about 2.4 per 1,000 population per year. Seasonal clustering has been observed, particularly in cases associated with sarcoidosis, with peaks in late summer and early autumn.
Genetic predisposition has been suggested, especially in sarcoidosis-associated cases, where specific human leukocyte antigens such as HLA-B8 and HLA-DR3 have been implicated.
Pathophysiologically, erythema nodosum is considered a type IV delayed hypersensitivity reaction to various antigens. This immune-mediated process leads to inflammation of the subcutaneous fat, particularly affecting the septa between fat lobules.
The etiology is diverse and includes infectious and noninfectious causes. Among infectious triggers, streptococcal infections (especially group A beta-hemolytic streptococci) are the most common. Other bacterial causes include tuberculosis, brucellosis, and cat-scratch disease. Viral causes include cytomegalovirus, Epstein–Barr virus, HIV, hepatitis B, and herpes simplex virus. Fungal infections such as histoplasmosis and coccidioidomycosis, as well as protozoal infections like toxoplasmosis and amebiasis, have also been implicated.
Noninfectious causes include medications (e.g., sulfonamides and oral contraceptives), malignancies (such as lymphoma and leukemia), and systemic diseases including sarcoidosis, inflammatory bowel disease, Behçet’s disease, lupus erythematosus, and Sjögren’s syndrome. Pregnancy is another recognized trigger. In many cases, however, no cause is identified (idiopathic erythema nodosum).
Clinically, patients present with the sudden onset of painful, erythematous nodules, most commonly on the shins, ankles, and knees. These lesions may be accompanied by systemic symptoms such as fever, fatigue, and joint pain. The nodules evolve over time, changing from bright red to purplish and eventually yellow-green, resembling bruises. Importantly, they do not ulcerate and heal without scarring.
On physical examination, the nodules are tender and raised initially, later becoming flatter as they resolve. They are most commonly located on the anterior lower legs but may also appear on the arms, neck, or face in rare cases.
Diagnosis is largely clinical but supported by investigations aimed at identifying the underlying cause. Laboratory tests include complete blood count, inflammatory markers (ESR), antistreptolysin O titers, throat cultures, and PCR for streptococcal infection. Tuberculosis testing and urinalysis may also be performed. Imaging such as chest X-ray is useful, particularly to detect sarcoidosis (e.g., bilateral hilar lymphadenopathy) or tuberculosis.
Additional diagnostic procedures may include stool studies for gastrointestinal symptoms, skin biopsy (which shows characteristic “Miescher’s radial granulomas”), and further investigations such as colonoscopy or lung biopsy depending on suspected underlying disease.
The differential diagnosis includes other forms of panniculitis such as erythema induratum of Bazin, superficial thrombophlebitis, Lyme disease, and systemic lupus erythematosus.
Management is primarily supportive, as erythema nodosum is usually self-limiting and resolves within a few weeks. Treatment should focus on addressing the underlying cause when identified. Symptomatic relief can be achieved with nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin or naproxen. In more severe cases, corticosteroids (e.g., prednisone) may be used after excluding infections and malignancy. Other therapies, including potassium iodide, hydroxychloroquine, colchicine, or biologics like infliximab, may be considered in specific cases.
General supportive measures include bed rest, leg elevation, and compression therapy to reduce discomfort and inflammation.
The prognosis is generally excellent, with most cases resolving within 3–4 weeks. Recurrence is uncommon but may occur, particularly in idiopathic cases or those associated with recurrent infections.
Complications are rare but may include unusual manifestations such as optic neuritis during acute episodes.
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Infectious Disease And Microbiology – Epiglottitis
Epiglottitis is a rapidly progressive and potentially life-threatening infection of the epiglottis and surrounding supraglottic structures. It is considered a medical emergency because it can lead to sudden airway obstruction and respiratory failure if not promptly recognized and treated.
The incidence of epiglottitis has declined significantly in countries with widespread vaccination against Haemophilus influenzae type b (Hib). However, it still occurs, particularly in adults, with an incidence of approximately 0.9–3.1 cases per 100,000 individuals. The average age of affected adults is around 45 years. Risk factors include young age (especially under 4 years), lack of vaccination, immunodeficiency, post-splenectomy status, and nonimmune adults. In the post-vaccination era, the average age of affected children has increased.
Prevention primarily involves immunization against H. influenzae type b. In cases where a patient has confirmed Hib epiglottitis and there are unvaccinated children under 4 years in the household, rifampin prophylaxis is recommended for all household members and the patient to eliminate bacterial carriage.
The most common causative organism in children remains H. influenzae type b, accounting for over 90% of pediatric cases. In adults, a wider range of pathogens may be involved, including Streptococcus pneumoniae, group A streptococci, Staphylococcus aureus, and Haemophilus parainfluenzae. In immunocompromised patients, fungal organisms such as Candida and Aspergillus may be implicated. Viral infections, including varicella-zoster virus, herpes simplex virus, HIV, and infectious mononucleosis, may also be associated with epiglottitis.
Clinically, the onset is usually acute. Children typically present within 24 hours with fever, difficulty speaking (dysphonia), difficulty swallowing (dysphagia), irritability, and drooling. Adults may have a less dramatic presentation, often with severe sore throat disproportionate to physical findings and sometimes without fever.
On physical examination, patients may exhibit respiratory distress, inspiratory stridor, and a characteristic muffled “hot potato” voice. Children often adopt a tripod position—sitting upright, leaning forward, and extending the neck—to maximize airway patency. Drooling is common due to difficulty swallowing. Severe cases may present with cyanosis, shock, or altered consciousness. Direct examination of the throat with a tongue depressor in children should be avoided, as it may trigger laryngospasm and complete airway obstruction.
Diagnosis should prioritize airway safety. Laboratory findings may show leukocytosis, and blood or epiglottic cultures may identify the causative organism. Imaging, such as a lateral neck X-ray, may reveal the classic “thumb sign” indicating a swollen epiglottis, but should only be performed when airway management is immediately available. Definitive diagnosis is made by visualization of a swollen, erythematous (“cherry-red”) epiglottis using fiberoptic laryngoscopy in a controlled setting.
The differential diagnosis includes croup, diphtheria, allergic laryngeal edema, foreign-body aspiration, peritonsillar abscess, and retropharyngeal abscess. Croup typically has a more gradual onset and lacks significant drooling, while diphtheria presents with a characteristic pseudomembrane.
Management of epiglottitis is an emergency focused on securing the airway. In children, early intubation is strongly recommended, as observation alone carries a high risk of mortality. If intubation is not possible, an emergency tracheostomy or cricothyrotomy may be required. Adults may sometimes be managed more conservatively, but any signs of respiratory compromise necessitate airway intervention.
Intravenous antibiotic therapy should be initiated promptly, targeting likely pathogens, particularly H. influenzae. Recommended regimens include ceftriaxone, cefotaxime, or ampicillin-sulbactam for approximately 10 days. The use of chloramphenicol is now rare due to toxicity. There is insufficient evidence to support routine use of corticosteroids or epinephrine.
All patients require hospital admission, often to an intensive care unit, for close monitoring. Airway stability is the primary concern during initial management, and intravenous fluids are frequently required. In children, intravenous access should not be attempted before securing the airway to avoid provoking distress.
Patients typically show rapid clinical improvement within 12–48 hours after starting appropriate therapy. Extubation can be considered once the patient is afebrile, clinically stable, and has evidence of reduced airway edema on examination. Adults managed without intubation require close ICU monitoring.
The prognosis largely depends on early airway management. Mortality is low when treated promptly but increases significantly if airway obstruction occurs. Rarely, recurrence may occur.
Complications include complete airway obstruction leading to hypoxia and potential brain injury, bacteremia with metastatic infections such as meningitis or arthritis, and complications related to airway management such as aspiration, pneumothorax, or tracheal injury.
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Infectious Disease And Microbiology – Epididymitis
Epididymitis is an inflammatory condition of the epididymis, most commonly caused by infection but also occasionally due to noninfectious causes such as trauma, drugs, or systemic diseases. It can be classified as acute or chronic, with chronic epididymitis defined by symptoms lasting more than three months.
Epididymitis is a common urologic condition, particularly in men aged 18–50 years, and is one of the leading causes of scrotal pain in this age group. It shows a bimodal age distribution, affecting younger sexually active men (16–30 years) and older men (51–70 years). It is also more common in men who engage in unprotected anal intercourse. Additional risk factors include bacteriuria, recent urinary tract instrumentation or surgery, prolonged sitting, strenuous physical activity, and conditions such as prostatic obstruction in older men or congenital urinary abnormalities in children.
Prevention focuses mainly on reducing sexually transmitted infections (STIs). This includes abstinence, mutual monogamy with an uninfected partner, and consistent and correct use of latex condoms. These measures significantly reduce the risk of infection-related epididymitis.
The pathophysiology typically involves retrograde ascent of pathogens from the urethra or bladder into the epididymis. Increased voiding pressures and urinary reflux into the vas deferens may contribute, especially in patients with underlying voiding dysfunction such as urethral strictures or bladder outlet obstruction.
The causes of epididymitis vary by age and risk factors. In younger men, the most common causes are sexually transmitted pathogens, particularly Neisseria gonorrhoeae and Chlamydia trachomatis. In older men or those with urinary tract abnormalities, enteric organisms such as Escherichia coli, Klebsiella, Proteus, and Pseudomonas are more common. Less frequently, infections may be caused by organisms such as Mycobacterium tuberculosis, Brucella, fungi, or parasites. Noninfectious causes include vasculitic diseases, medications like amiodarone, trauma, or idiopathic mechanisms. Epididymitis is often associated with orchitis (inflammation of the testis).
Clinically, patients typically present with gradual onset of unilateral scrotal pain and swelling over several days. Pain is usually localized to the posterior aspect of the testis and may radiate to the lower abdomen. Urinary symptoms such as dysuria, frequency, urgency, or hematuria may be present, along with fever and chills. A preceding urethral discharge suggests a sexually transmitted cause. Chronic epididymitis presents with persistent or intermittent discomfort lasting more than six weeks.
On physical examination, there is localized tenderness of the epididymis that may progress to testicular swelling. Urethral discharge may be visible. The cremasteric reflex is usually preserved, which helps distinguish epididymitis from testicular torsion. Pain may improve with elevation of the testis (Prehn’s sign). In advanced cases, reactive hydrocele or scrotal erythema may develop.
Diagnosis involves laboratory and imaging studies. Urethral swabs and urine samples are used to detect infection, including Gram stain, culture, and PCR testing for Chlamydia and Gonorrhea. Urinalysis may show leukocytes or leukocyte esterase. Blood cultures may be useful in severe cases. Inflammatory markers such as CRP and ESR may help differentiate epididymitis from testicular torsion. Color Doppler ultrasonography is the imaging modality of choice and typically shows increased blood flow in the epididymis, helping to exclude torsion, which shows reduced flow.
The main differential diagnosis is testicular torsion, which is a surgical emergency and must always be excluded. Other less common considerations include testicular tumors.
Treatment is primarily medical. Empiric antibiotic therapy should be started promptly based on the most likely pathogens. In sexually transmitted cases, treatment includes a single intramuscular dose of ceftriaxone followed by oral doxycycline for 10 days, or azithromycin as an alternative. In cases due to enteric organisms, fluoroquinolones such as levofloxacin or ofloxacin are commonly used. Supportive measures include bed rest, scrotal elevation, analgesics, and nonsteroidal anti-inflammatory drugs. Patients with HIV are treated similarly, although atypical pathogens may be more common.
Surgical intervention is reserved for complications such as abscess formation, testicular infarction, or pyocele. Hospital admission is required for severe cases with systemic symptoms or suspected bacteremia.
Patient education is essential. Patients with sexually transmitted epididymitis should ensure that their sexual partners are evaluated and treated if exposure occurred within the preceding 60 days. Sexual activity should be avoided until treatment is completed and symptoms have resolved.
Complications include bacteremia, testicular infarction, scrotal abscess, chronic epididymitis, infertility, and formation of a draining sinus. In children, distinguishing epididymitis from testicular torsion is especially important, as torsion is more common and requires urgent surgical management.
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Infectious Disease And Microbiology – Epidemic Pleurodynia (Bornholm Disease)
Epidemic pleurodynia is an acute febrile illness characterized by the sudden onset of severe chest or abdominal pain accompanied by muscle spasms. It is also known as epidemic myalgia or Bornholm disease, named after a Danish island where outbreaks were first described, and is sometimes referred to as “devil’s grip” due to the intensity of pain.
This condition typically occurs in outbreaks, often affecting multiple members of the same household or community either simultaneously or over several days. It is most commonly caused by enteroviruses, particularly coxsackievirus group B, though coxsackievirus A and echoviruses can also be responsible. The disease is more prevalent during late summer and early autumn, coinciding with peak enteroviral transmission. Close contact in settings such as sports fields, locker rooms, or shared drinking containers facilitates person-to-person spread. Children tend to experience milder illness than adults, though infections can also occur in neonates. Intense physical exertion during the incubation period may lead to more severe symptoms.
Prevention focuses on limiting transmission through good hygiene practices. Avoiding shared oral contact, using individual drinking containers, and preventing contamination of shared items such as ice chests are important measures. Education of students, athletes, and staff in group settings can help reduce outbreaks.
The pathophysiology is thought to involve direct viral invasion of skeletal muscles of the thoracic and abdominal wall, leading to inflammation and pain. The most common etiologic agent is coxsackievirus B, although several echoviruses and coxsackievirus A strains have also been implicated.
Clinically, the illness begins abruptly without a prodrome, with fever and severe, intermittent spasms of pleuritic chest or upper abdominal pain. Fever typically rises quickly to 38–39.5°C and subsides as the pain resolves. The pain is sharp, stabbing, and often described as knifelike, lasting 15–30 minutes per episode and associated with sweating and rapid breathing. In adults, chest pain predominates, while children more commonly present with abdominal pain, sometimes mimicking acute surgical conditions. Muscle tenderness is usually present, and a pleural rub may occasionally be heard. The illness generally lasts 4–6 days, although duration may vary.
On physical examination, pain can typically be reproduced by palpation of the affected muscles, and in some cases, localized swelling may be noted. Laboratory findings are usually nonspecific, with a normal white blood cell count. Virologic confirmation can be achieved by isolating the virus from throat swabs or stool samples, or by demonstrating rising antibody titers. Chest imaging is typically normal, although small pleural effusions may rarely be seen.
The differential diagnosis is broad and includes pneumonia, pulmonary embolism, myocardial ischemia, pulmonary infarction, herpes zoster, and causes of acute abdominal pain such as appendicitis or renal colic. Because of its dramatic presentation, careful evaluation is needed to exclude these more serious conditions.
Treatment is primarily supportive. Nonsteroidal anti-inflammatory drugs are the mainstay for pain relief, and application of heat to the affected muscles can provide additional comfort. In severe cases, opiate analgesics may be required. General supportive care is usually sufficient, and no specific antiviral therapy is indicated.
The prognosis is excellent. The illness is self-limited, typically resolving within 4–7 days, and is rarely fatal. Recurrences can occur but are uncommon. Complications are rare but may include aseptic meningitis or orchitis in a small percentage of cases, while pericarditis and pneumonia are even less frequently observed.
Epidemic pleurodynia is an acute febrile illness characterized by the sudden onset of severe chest or abdominal pain accompanied by muscle spasms. It is also known as epidemic myalgia or Bornholm disease, named after a Danish island where outbreaks were first described, and is sometimes referred to as “devil’s grip” due to the intensity of pain.
This condition typically occurs in outbreaks, often affecting multiple members of the same household or community either simultaneously or over several days. It is most commonly caused by enteroviruses, particularly coxsackievirus group B, though coxsackievirus A and echoviruses can also be responsible. The disease is more prevalent during late summer and early autumn, coinciding with peak enteroviral transmission. Close contact in settings such as sports fields, locker rooms, or shared drinking containers facilitates person-to-person spread. Children tend to experience milder illness than adults, though infections can also occur in neonates. Intense physical exertion during the incubation period may lead to more severe symptoms.
Prevention focuses on limiting transmission through good hygiene practices. Avoiding shared oral contact, using individual drinking containers, and preventing contamination of shared items such as ice chests are important measures. Education of students, athletes, and staff in group settings can help reduce outbreaks.
The pathophysiology is thought to involve direct viral invasion of skeletal muscles of the thoracic and abdominal wall, leading to inflammation and pain. The most common etiologic agent is coxsackievirus B, although several echoviruses and coxsackievirus A strains have also been implicated.
Clinically, the illness begins abruptly without a prodrome, with fever and severe, intermittent spasms of pleuritic chest or upper abdominal pain. Fever typically rises quickly to 38–39.5°C and subsides as the pain resolves. The pain is sharp, stabbing, and often described as knifelike, lasting 15–30 minutes per episode and associated with sweating and rapid breathing. In adults, chest pain predominates, while children more commonly present with abdominal pain, sometimes mimicking acute surgical conditions. Muscle tenderness is usually present, and a pleural rub may occasionally be heard. The illness generally lasts 4–6 days, although duration may vary.
On physical examination, pain can typically be reproduced by palpation of the affected muscles, and in some cases, localized swelling may be noted. Laboratory findings are usually nonspecific, with a normal white blood cell count. Virologic confirmation can be achieved by isolating the virus from throat swabs or stool samples, or by demonstrating rising antibody titers. Chest imaging is typically normal, although small pleural effusions may rarely be seen.
The differential diagnosis is broad and includes pneumonia, pulmonary embolism, myocardial ischemia, pulmonary infarction, herpes zoster, and causes of acute abdominal pain such as appendicitis or renal colic. Because of its dramatic presentation, careful evaluation is needed to exclude these more serious conditions.
Treatment is primarily supportive. Nonsteroidal anti-inflammatory drugs are the mainstay for pain relief, and application of heat to the affected muscles can provide additional comfort. In severe cases, opiate analgesics may be required. General supportive care is usually sufficient, and no specific antiviral therapy is indicated.
The prognosis is excellent. The illness is self-limited, typically resolving within 4–7 days, and is rarely fatal. Recurrences can occur but are uncommon. Complications are rare but may include aseptic meningitis or orchitis in a small percentage of cases, while pericarditis and pneumonia are even less frequently observed.
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Infectious Disease And Microbiology – Endophthalmitis
Endophthalmitis is a severe infectious condition involving the ocular (vitreous) cavity, while panophthalmitis refers to inflammation affecting all structures of the eye. It is a vision-threatening emergency most commonly occurring after ocular surgery, trauma, or via hematogenous spread from a distant infection.
The incidence of endophthalmitis after cataract surgery ranges from 0.1–0.3%, whereas it is significantly higher after penetrating ocular trauma (3–30%), especially when intraocular foreign bodies are present. Major risk factors include untreated eyelid disease (such as blepharitis), poor surgical technique, prolonged operative time, and intraoperative complications. Endogenous endophthalmitis is more likely in chronically ill, diabetic, or immunocompromised patients, particularly those with indwelling intravenous catheters or bloodstream infections.
Prevention strategies include routine postoperative use of topical fluoroquinolones after cataract surgery, although definitive evidence of benefit is limited. Intracameral cefuroxime has been shown to reduce postoperative risk. In high-risk penetrating ocular injuries, systemic prophylaxis with vancomycin or moxifloxacin may be used. For anterior segment trauma, intensive topical antibiotics or subconjunctival injections may achieve adequate antimicrobial levels. Patients with systemic infections, especially fungemia due to Candida species, should be monitored for possible endogenous spread to the eye.
The pathophysiology differs depending on the source. In postoperative cases, organisms from the eyelid or conjunctiva may enter through surgical wounds. In endogenous cases, pathogens disseminate hematogenously and initially involve the choroid before extending into the vitreous cavity.
Endophthalmitis may be caused by bacteria, fungi, or parasites. Common bacterial pathogens include Staphylococcus, Streptococcus, Pseudomonas, and Escherichia coli. Fungal causes include Candida, Aspergillus, and Fusarium. Parasitic causes include Taenia solium, Toxocara canis, and Toxoplasma gondii. Acute postoperative cases are most often due to Gram-positive organisms, whereas more severe infections and worse outcomes are associated with Gram-negative bacteria and streptococci. Trauma-related infections frequently involve mixed organisms, especially in rural injuries contaminated with organic material.
Clinically, most patients present with ocular pain, redness (conjunctival injection), photophobia, and reduced vision. In some cases, visual loss may be the only symptom. More aggressive infections, such as those caused by Bacillus cereus, can present rapidly with severe pain and profound vision loss. Panophthalmitis may cause pain with eye movement.
On examination, key findings include vitreous opacities, which are essential for diagnosis, and hypopyon (layering of white blood cells in the anterior chamber). Chorioretinal infiltrates are characteristic of endogenous infection.
Diagnosis involves obtaining aqueous and vitreous samples for microscopy and culture. Smears should be stained using Gram, Giemsa, and special fungal stains, and cultured for aerobic and anaerobic bacteria, mycobacteria, and fungi. Culture positivity is approximately 70% in postoperative cases. Imaging with ocular ultrasonography or CT scan is useful when visualization is limited or when a retained intraocular foreign body is suspected.
The differential diagnosis includes noninfectious causes such as uveitis, toxic anterior segment syndrome (TASS), and sterile postoperative inflammation due to retained lens fragments.
Management is an ophthalmologic emergency requiring immediate treatment. First-line therapy for acute postoperative bacterial endophthalmitis includes intravitreal injection of vancomycin for Gram-positive coverage and ceftazidime (or amikacin in β-lactam allergy) for Gram-negative coverage. Intensive topical antibiotics are also used. Systemic antibiotics are generally not beneficial in routine postoperative cases but may be considered with newer fluoroquinolones due to good ocular penetration.
In endogenous endophthalmitis, systemic antimicrobial therapy targeting the primary source is essential in addition to intravitreal treatment. For fungal infections, intravitreal amphotericin B is commonly used, though retinal toxicity must be considered. Systemic antifungal therapy is required in endogenous disease, with alternatives such as fluconazole, voriconazole, or caspofungin.
Supportive treatment includes pain management and cycloplegic eye drops. Corticosteroids may be used topically or periocularly to reduce inflammation, although systemic or intravitreal use remains controversial. Early referral to an ophthalmologist is critical.
Surgical intervention with pars plana vitrectomy is indicated in severe cases, especially when visual acuity is limited to light perception or worse. This procedure helps remove infectious material, toxins, and inflammatory debris, thereby improving outcomes.
Patients are typically managed as outpatients unless special circumstances require admission. Close daily follow-up is essential. If there is no improvement or worsening within 48 hours, repeat intravitreal antibiotics and/or vitrectomy should be considered.
Prognosis varies depending on the cause. Postoperative endophthalmitis has better outcomes than traumatic cases. After cataract surgery, approximately 50% of patients may achieve visual acuity of 20/40 or better, while outcomes are poorer in traumatic infections. Infections caused by Bacillus cereus have a particularly poor prognosis. Complications include permanent vision loss, retinal detachment, secondary glaucoma, and phthisis bulbi.
Endophthalmitis is a severe infectious condition involving the ocular (vitreous) cavity, while panophthalmitis refers to inflammation affecting all structures of the eye. It is a vision-threatening emergency most commonly occurring after ocular surgery, trauma, or via hematogenous spread from a distant infection.
The incidence of endophthalmitis after cataract surgery ranges from 0.1–0.3%, whereas it is significantly higher after penetrating ocular trauma (3–30%), especially when intraocular foreign bodies are present. Major risk factors include untreated eyelid disease (such as blepharitis), poor surgical technique, prolonged operative time, and intraoperative complications. Endogenous endophthalmitis is more likely in chronically ill, diabetic, or immunocompromised patients, particularly those with indwelling intravenous catheters or bloodstream infections.
Prevention strategies include routine postoperative use of topical fluoroquinolones after cataract surgery, although definitive evidence of benefit is limited. Intracameral cefuroxime has been shown to reduce postoperative risk. In high-risk penetrating ocular injuries, systemic prophylaxis with vancomycin or moxifloxacin may be used. For anterior segment trauma, intensive topical antibiotics or subconjunctival injections may achieve adequate antimicrobial levels. Patients with systemic infections, especially fungemia due to Candida species, should be monitored for possible endogenous spread to the eye.
The pathophysiology differs depending on the source. In postoperative cases, organisms from the eyelid or conjunctiva may enter through surgical wounds. In endogenous cases, pathogens disseminate hematogenously and initially involve the choroid before extending into the vitreous cavity.
Endophthalmitis may be caused by bacteria, fungi, or parasites. Common bacterial pathogens include Staphylococcus, Streptococcus, Pseudomonas, and Escherichia coli. Fungal causes include Candida, Aspergillus, and Fusarium. Parasitic causes include Taenia solium, Toxocara canis, and Toxoplasma gondii. Acute postoperative cases are most often due to Gram-positive organisms, whereas more severe infections and worse outcomes are associated with Gram-negative bacteria and streptococci. Trauma-related infections frequently involve mixed organisms, especially in rural injuries contaminated with organic material.
Clinically, most patients present with ocular pain, redness (conjunctival injection), photophobia, and reduced vision. In some cases, visual loss may be the only symptom. More aggressive infections, such as those caused by Bacillus cereus, can present rapidly with severe pain and profound vision loss. Panophthalmitis may cause pain with eye movement.
On examination, key findings include vitreous opacities, which are essential for diagnosis, and hypopyon (layering of white blood cells in the anterior chamber). Chorioretinal infiltrates are characteristic of endogenous infection.
Diagnosis involves obtaining aqueous and vitreous samples for microscopy and culture. Smears should be stained using Gram, Giemsa, and special fungal stains, and cultured for aerobic and anaerobic bacteria, mycobacteria, and fungi. Culture positivity is approximately 70% in postoperative cases. Imaging with ocular ultrasonography or CT scan is useful when visualization is limited or when a retained intraocular foreign body is suspected.
The differential diagnosis includes noninfectious causes such as uveitis, toxic anterior segment syndrome (TASS), and sterile postoperative inflammation due to retained lens fragments.
Management is an ophthalmologic emergency requiring immediate treatment. First-line therapy for acute postoperative bacterial endophthalmitis includes intravitreal injection of vancomycin for Gram-positive coverage and ceftazidime (or amikacin in β-lactam allergy) for Gram-negative coverage. Intensive topical antibiotics are also used. Systemic antibiotics are generally not beneficial in routine postoperative cases but may be considered with newer fluoroquinolones due to good ocular penetration.
In endogenous endophthalmitis, systemic antimicrobial therapy targeting the primary source is essential in addition to intravitreal treatment. For fungal infections, intravitreal amphotericin B is commonly used, though retinal toxicity must be considered. Systemic antifungal therapy is required in endogenous disease, with alternatives such as fluconazole, voriconazole, or caspofungin.
Supportive treatment includes pain management and cycloplegic eye drops. Corticosteroids may be used topically or periocularly to reduce inflammation, although systemic or intravitreal use remains controversial. Early referral to an ophthalmologist is critical.
Surgical intervention with pars plana vitrectomy is indicated in severe cases, especially when visual acuity is limited to light perception or worse. This procedure helps remove infectious material, toxins, and inflammatory debris, thereby improving outcomes.
Patients are typically managed as outpatients unless special circumstances require admission. Close daily follow-up is essential. If there is no improvement or worsening within 48 hours, repeat intravitreal antibiotics and/or vitrectomy should be considered.
Prognosis varies depending on the cause. Postoperative endophthalmitis has better outcomes than traumatic cases. After cataract surgery, approximately 50% of patients may achieve visual acuity of 20/40 or better, while outcomes are poorer in traumatic infections. Infections caused by Bacillus cereus have a particularly poor prognosis. Complications include permanent vision loss, retinal detachment, secondary glaucoma, and phthisis bulbi.
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Infectious Disease And Microbiology – Endocarditis (Prosthetic Valve)
Prosthetic valve endocarditis is an infection involving prosthetic heart valves or associated prosthetic material. It is most commonly caused by bacteria, especially Gram-positive organisms, although fungi and, rarely, organisms such as chlamydiae or rickettsiae may also be responsible. This form of endocarditis is a serious complication of valve replacement and can arise either early after surgery or later through bloodstream spread from another infectious source.
The incidence of prosthetic valve infective endocarditis is approximately 0.3–1% per patient-year. The most important risk factors are healthcare-associated infections, chronic intravascular access, and hemodialysis. Additional predisposing factors include the presence of prosthetic valve material itself and any circumstances that increase the likelihood of bloodstream infection.
Prevention includes antibiotic prophylaxis for high-risk patients, particularly before dental procedures that involve manipulation of gingival tissue or disruption of the oral mucosa. Prophylaxis is also considered reasonable for certain respiratory, skin, soft tissue, or muscle procedures in those at highest risk. Recommended prophylactic regimens include a single dose of amoxicillin 2 g or clindamycin 600 mg administered 30–60 minutes before the procedure. Antibiotic prophylaxis is not recommended for gastrointestinal or genitourinary procedures.
The pathophysiology of prosthetic valve endocarditis involves contamination during implantation, later hematogenous seeding of the prosthesis, or contiguous spread of nearby infection. Staphylococci are the most common causes. Early-onset prosthetic valve endocarditis, occurring within 60 days of surgery, is more often due to hospital-acquired pathogens, whereas late-onset infection is caused by organisms more similar to those seen in native valve endocarditis. Early infections are commonly caused by Staphylococcus aureus, coagulase-negative staphylococci, enterococci, Gram-negative bacilli, fungi, and occasionally streptococci. Late infections are more often caused by S. aureus, coagulase-negative staphylococci, streptococci, enterococci, fungi, and Gram-negative bacilli. Culture-negative cases may occur, most often after recent antibiotic exposure or with fastidious organisms such as Bartonella, Coxiella burnetii, Brucella, or Tropheryma whipplei.
The clinical presentation is highly variable. Some patients present with an acute toxic illness and high fever, whereas others have a more indolent subacute course. In any patient with a prosthetic valve and unexplained fever, endocarditis must be strongly considered. Fever is present in more than 70% of cases, and other symptoms may include weakness, chills, sweats, anorexia, weight loss, nausea, and malaise. A careful history should also explore travel, animal exposure, and consumption of unpasteurized dairy products, which may suggest unusual pathogens.
Diagnosis is commonly based on the modified Duke criteria, which combine clinical, microbiologic, and echocardiographic data. Major criteria include persistently positive blood cultures for typical organisms and evidence of endocardial involvement, such as vegetations, abscesses, prosthetic valve dehiscence, or new valvular regurgitation. Minor criteria include predisposition, fever, vascular phenomena, immunologic phenomena, and microbiologic findings that do not meet major criteria.
On physical examination, patients may have a new or changed murmur or signs of congestive heart failure. Because embolic and metastatic complications are common, a full examination should assess for neurologic deficits, splenic involvement, spinal tenderness, joint infection, or other distant sites of disease.
Initial laboratory workup includes complete blood count, electrolytes, renal and liver function tests, inflammatory markers, urinalysis, and multiple blood cultures. At least three sets of blood cultures should be obtained within the first 24 hours before starting antibiotics. The first two sets are positive in most patients. Leukocytosis and elevated ESR or CRP are common. In culture-negative cases, serologic testing for organisms such as Coxiella burnetii and Bartonella should be considered. Blood cultures should be repeated every 24–48 hours until the infection has cleared.
Transesophageal echocardiography is the imaging test of choice because prosthetic valves often create artifact on transthoracic studies and because prosthetic valve infections frequently involve paravalvular complications. TEE has high sensitivity and specificity for detecting vegetations, abscesses, and dehiscence and should be performed as soon as possible when prosthetic valve endocarditis is suspected. Additional imaging of the brain, lungs, abdomen, or spine may be needed if embolic events, abscesses, or mycotic aneurysms are suspected. Electrocardiography is also important to detect baseline or evolving conduction abnormalities, which may indicate abscess extension.
Treatment requires prolonged bactericidal intravenous antibiotic therapy, with regimens tailored to the causative organism and its susceptibilities. For streptococcal infections, treatment typically includes penicillin G or ceftriaxone plus gentamicin, with vancomycin used in selected allergic patients. For enterococci or highly penicillin-resistant streptococci, ampicillin plus gentamicin is commonly used, or vancomycin plus gentamicin if ampicillin cannot be given. Methicillin-susceptible staphylococcal infections are treated with nafcillin plus rifampin for at least six weeks, with gentamicin added for the first two weeks. Methicillin-resistant staphylococcal infections are treated with vancomycin plus rifampin for at least six weeks, again with gentamicin for two weeks. Rifampin is often delayed by a few days because resistance can develop quickly if started too early.
Management requires a multidisciplinary approach involving cardiology, infectious diseases, and cardiovascular surgery. Patients with prosthetic valve endocarditis should be evaluated early for surgery. Valve replacement may be necessary in cases of prosthetic valve dehiscence, perforation, fistula formation, large abscess, severe structural damage, or failure of medical therapy because of highly resistant organisms.
All patients require hospitalization for monitoring, intravenous therapy, and expedited evaluation. They may be discharged once fevers have resolved for more than 24 hours, vital signs are stable, and a safe plan for continued antibiotic treatment and follow-up is in place. During and after therapy, patients should be monitored closely for relapse, treatment complications, and new cardiac dysfunction. At completion of therapy, transthoracic echocardiography is recommended to establish a new baseline for valve and cardiac function.
Patient education is important and should include the importance of good oral hygiene, prevention of future endocarditis associated with dental procedures, and recognition of symptoms of valvular dysfunction. Prognosis depends on several factors. Higher mortality is associated with healthcare-associated infection, congestive heart failure, older age, S. aureus infection, persistent bacteremia, stroke, and intracardiac abscess. In-hospital mortality is substantial. Complications include periprosthetic leak, ring abscess, congestive heart failure, cerebral emboli, stroke, renal infarction, immune complex glomerulonephritis, mycotic aneurysm, meningitis, cerebritis, splenic infarction or abscess, heart block, and pulmonary embolism in right-sided disease.
Prosthetic valve endocarditis is an infection involving prosthetic heart valves or associated prosthetic material. It is most commonly caused by bacteria, especially Gram-positive organisms, although fungi and, rarely, organisms such as chlamydiae or rickettsiae may also be responsible. This form of endocarditis is a serious complication of valve replacement and can arise either early after surgery or later through bloodstream spread from another infectious source.
The incidence of prosthetic valve infective endocarditis is approximately 0.3–1% per patient-year. The most important risk factors are healthcare-associated infections, chronic intravascular access, and hemodialysis. Additional predisposing factors include the presence of prosthetic valve material itself and any circumstances that increase the likelihood of bloodstream infection.
Prevention includes antibiotic prophylaxis for high-risk patients, particularly before dental procedures that involve manipulation of gingival tissue or disruption of the oral mucosa. Prophylaxis is also considered reasonable for certain respiratory, skin, soft tissue, or muscle procedures in those at highest risk. Recommended prophylactic regimens include a single dose of amoxicillin 2 g or clindamycin 600 mg administered 30–60 minutes before the procedure. Antibiotic prophylaxis is not recommended for gastrointestinal or genitourinary procedures.
The pathophysiology of prosthetic valve endocarditis involves contamination during implantation, later hematogenous seeding of the prosthesis, or contiguous spread of nearby infection. Staphylococci are the most common causes. Early-onset prosthetic valve endocarditis, occurring within 60 days of surgery, is more often due to hospital-acquired pathogens, whereas late-onset infection is caused by organisms more similar to those seen in native valve endocarditis. Early infections are commonly caused by Staphylococcus aureus, coagulase-negative staphylococci, enterococci, Gram-negative bacilli, fungi, and occasionally streptococci. Late infections are more often caused by S. aureus, coagulase-negative staphylococci, streptococci, enterococci, fungi, and Gram-negative bacilli. Culture-negative cases may occur, most often after recent antibiotic exposure or with fastidious organisms such as Bartonella, Coxiella burnetii, Brucella, or Tropheryma whipplei.
The clinical presentation is highly variable. Some patients present with an acute toxic illness and high fever, whereas others have a more indolent subacute course. In any patient with a prosthetic valve and unexplained fever, endocarditis must be strongly considered. Fever is present in more than 70% of cases, and other symptoms may include weakness, chills, sweats, anorexia, weight loss, nausea, and malaise. A careful history should also explore travel, animal exposure, and consumption of unpasteurized dairy products, which may suggest unusual pathogens.
Diagnosis is commonly based on the modified Duke criteria, which combine clinical, microbiologic, and echocardiographic data. Major criteria include persistently positive blood cultures for typical organisms and evidence of endocardial involvement, such as vegetations, abscesses, prosthetic valve dehiscence, or new valvular regurgitation. Minor criteria include predisposition, fever, vascular phenomena, immunologic phenomena, and microbiologic findings that do not meet major criteria.
On physical examination, patients may have a new or changed murmur or signs of congestive heart failure. Because embolic and metastatic complications are common, a full examination should assess for neurologic deficits, splenic involvement, spinal tenderness, joint infection, or other distant sites of disease.
Initial laboratory workup includes complete blood count, electrolytes, renal and liver function tests, inflammatory markers, urinalysis, and multiple blood cultures. At least three sets of blood cultures should be obtained within the first 24 hours before starting antibiotics. The first two sets are positive in most patients. Leukocytosis and elevated ESR or CRP are common. In culture-negative cases, serologic testing for organisms such as Coxiella burnetii and Bartonella should be considered. Blood cultures should be repeated every 24–48 hours until the infection has cleared.
Transesophageal echocardiography is the imaging test of choice because prosthetic valves often create artifact on transthoracic studies and because prosthetic valve infections frequently involve paravalvular complications. TEE has high sensitivity and specificity for detecting vegetations, abscesses, and dehiscence and should be performed as soon as possible when prosthetic valve endocarditis is suspected. Additional imaging of the brain, lungs, abdomen, or spine may be needed if embolic events, abscesses, or mycotic aneurysms are suspected. Electrocardiography is also important to detect baseline or evolving conduction abnormalities, which may indicate abscess extension.
Treatment requires prolonged bactericidal intravenous antibiotic therapy, with regimens tailored to the causative organism and its susceptibilities. For streptococcal infections, treatment typically includes penicillin G or ceftriaxone plus gentamicin, with vancomycin used in selected allergic patients. For enterococci or highly penicillin-resistant streptococci, ampicillin plus gentamicin is commonly used, or vancomycin plus gentamicin if ampicillin cannot be given. Methicillin-susceptible staphylococcal infections are treated with nafcillin plus rifampin for at least six weeks, with gentamicin added for the first two weeks. Methicillin-resistant staphylococcal infections are treated with vancomycin plus rifampin for at least six weeks, again with gentamicin for two weeks. Rifampin is often delayed by a few days because resistance can develop quickly if started too early.
Management requires a multidisciplinary approach involving cardiology, infectious diseases, and cardiovascular surgery. Patients with prosthetic valve endocarditis should be evaluated early for surgery. Valve replacement may be necessary in cases of prosthetic valve dehiscence, perforation, fistula formation, large abscess, severe structural damage, or failure of medical therapy because of highly resistant organisms.
All patients require hospitalization for monitoring, intravenous therapy, and expedited evaluation. They may be discharged once fevers have resolved for more than 24 hours, vital signs are stable, and a safe plan for continued antibiotic treatment and follow-up is in place. During and after therapy, patients should be monitored closely for relapse, treatment complications, and new cardiac dysfunction. At completion of therapy, transthoracic echocardiography is recommended to establish a new baseline for valve and cardiac function.
Patient education is important and should include the importance of good oral hygiene, prevention of future endocarditis associated with dental procedures, and recognition of symptoms of valvular dysfunction. Prognosis depends on several factors. Higher mortality is associated with healthcare-associated infection, congestive heart failure, older age, S. aureus infection, persistent bacteremia, stroke, and intracardiac abscess. In-hospital mortality is substantial. Complications include periprosthetic leak, ring abscess, congestive heart failure, cerebral emboli, stroke, renal infarction, immune complex glomerulonephritis, mycotic aneurysm, meningitis, cerebritis, splenic infarction or abscess, heart block, and pulmonary embolism in right-sided disease.
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Infectious Disease And Microbiology – Endocarditis (Native Valves)
Endocarditis is an infection of the endocardial surface of the heart, most commonly involving the heart valves. It is typically caused by bacteria, though fungi and, rarely, organisms such as chlamydiae or rickettsiae may be responsible. In native valve infective endocarditis (NVIE), the mitral valve is most frequently affected, followed by the aortic valve. The tricuspid valve is more commonly involved in individuals who use intravenous drugs, while pulmonic valve involvement is rare. In some cases, multiple valves may be infected simultaneously.
The incidence of NVIE ranges from approximately 1.7 to 6.2 cases per 100,000 person-years, but is significantly higher among intravenous drug users. Risk factors include intravenous drug use, prior history of endocarditis, chronic intravascular access, implanted cardiac devices, congenital heart disease, bicuspid aortic valve, rheumatic heart disease, and degenerative valvular disease. Preventive strategies include antibiotic prophylaxis for high-risk individuals—such as those with prosthetic valves, prior endocarditis, certain congenital heart diseases, or cardiac transplant recipients with valvulopathy—especially before dental procedures involving manipulation of the gingiva or oral mucosa.
The most common causative organisms are Gram-positive bacteria, with Staphylococcus aureus now being the leading cause of NVIE. Other important pathogens include viridans group streptococci, Streptococcus bovis, enterococci, coagulase-negative staphylococci, and the HACEK group of organisms. Fungal infections account for a smaller proportion of cases. Approximately 10% of cases are culture-negative, often due to prior antibiotic use or infection with fastidious organisms such as Bartonella or Coxiella burnetii.
Clinically, NVIE presents with a wide range of symptoms resulting from valvular infection, embolic phenomena, metastatic infection, and immune complex deposition. Fever is present in over 90% of patients, along with nonspecific symptoms such as malaise, fatigue, weight loss, and chills. The modified Duke criteria are widely used for diagnosis and incorporate clinical, microbiological, and echocardiographic findings. Major criteria include positive blood cultures with typical organisms and evidence of endocardial involvement on echocardiography, while minor criteria include fever, predisposing conditions, vascular and immunologic phenomena, and less specific microbiologic evidence.
On physical examination, a new or changing heart murmur is found in the majority of patients. Other findings may include petechiae, splinter hemorrhages, Osler nodes, Janeway lesions, and Roth spots, although these are less common. A thorough examination is necessary to detect complications such as embolic events or metastatic infections.
Diagnosis requires prompt laboratory and imaging evaluation. Blood cultures are critical and should be obtained before starting antibiotics, with at least three sets drawn within the first 24 hours. Most cases can be diagnosed based on positive blood cultures. Laboratory findings often include leukocytosis, elevated inflammatory markers, and abnormalities on urinalysis such as hematuria or proteinuria. In cases of culture-negative endocarditis, serologic testing for atypical organisms may be necessary.
Echocardiography is the imaging modality of choice. Transthoracic echocardiography (TTE) is often used initially, but transesophageal echocardiography (TEE) is more sensitive and is preferred when clinical suspicion is high or when TTE results are inconclusive. Imaging may reveal vegetations, abscesses, or valvular dysfunction. Additional imaging studies may be required to evaluate for embolic complications or abscess formation in other organs.
Treatment involves prolonged intravenous bactericidal antibiotic therapy tailored to the causative organism and its antimicrobial susceptibilities. Empiric therapy is initiated based on clinical suspicion and risk factors. Common regimens include penicillin or ceftriaxone for streptococcal infections, ampicillin with gentamicin for enterococci, and nafcillin or vancomycin for Staphylococcus aureus. Therapy typically lasts several weeks to ensure eradication of infection within vegetations.
Surgical intervention is required in approximately 30–50% of cases and is considered in patients with heart failure, uncontrolled infection, large vegetations with recurrent emboli, or complications such as abscess formation. Management often requires a multidisciplinary approach involving cardiology, infectious diseases, and cardiac surgery teams.
Patients with endocarditis require hospitalization for initiation of treatment and close monitoring. Follow-up includes repeated blood cultures to confirm clearance of infection, monitoring for complications, and echocardiography to assess cardiac function after treatment. Patient education is important, particularly regarding oral hygiene and prevention of future infections.
The prognosis of NVIE depends on multiple factors, including the causative organism, patient comorbidities, and presence of complications. Mortality remains significant, with rates approaching 40% at one year. Poor prognostic factors include heart failure, infection with Staphylococcus aureus, older age, immunosuppression, and extension of infection beyond the valve. Complications include heart failure, stroke, systemic emboli, renal infarction, glomerulonephritis, mycotic aneurysms, and metastatic infections such as splenic abscess or meningitis.
Endocarditis is an infection of the endocardial surface of the heart, most commonly involving the heart valves. It is typically caused by bacteria, though fungi and, rarely, organisms such as chlamydiae or rickettsiae may be responsible. In native valve infective endocarditis (NVIE), the mitral valve is most frequently affected, followed by the aortic valve. The tricuspid valve is more commonly involved in individuals who use intravenous drugs, while pulmonic valve involvement is rare. In some cases, multiple valves may be infected simultaneously.
The incidence of NVIE ranges from approximately 1.7 to 6.2 cases per 100,000 person-years, but is significantly higher among intravenous drug users. Risk factors include intravenous drug use, prior history of endocarditis, chronic intravascular access, implanted cardiac devices, congenital heart disease, bicuspid aortic valve, rheumatic heart disease, and degenerative valvular disease. Preventive strategies include antibiotic prophylaxis for high-risk individuals—such as those with prosthetic valves, prior endocarditis, certain congenital heart diseases, or cardiac transplant recipients with valvulopathy—especially before dental procedures involving manipulation of the gingiva or oral mucosa.
The most common causative organisms are Gram-positive bacteria, with Staphylococcus aureus now being the leading cause of NVIE. Other important pathogens include viridans group streptococci, Streptococcus bovis, enterococci, coagulase-negative staphylococci, and the HACEK group of organisms. Fungal infections account for a smaller proportion of cases. Approximately 10% of cases are culture-negative, often due to prior antibiotic use or infection with fastidious organisms such as Bartonella or Coxiella burnetii.
Clinically, NVIE presents with a wide range of symptoms resulting from valvular infection, embolic phenomena, metastatic infection, and immune complex deposition. Fever is present in over 90% of patients, along with nonspecific symptoms such as malaise, fatigue, weight loss, and chills. The modified Duke criteria are widely used for diagnosis and incorporate clinical, microbiological, and echocardiographic findings. Major criteria include positive blood cultures with typical organisms and evidence of endocardial involvement on echocardiography, while minor criteria include fever, predisposing conditions, vascular and immunologic phenomena, and less specific microbiologic evidence.
On physical examination, a new or changing heart murmur is found in the majority of patients. Other findings may include petechiae, splinter hemorrhages, Osler nodes, Janeway lesions, and Roth spots, although these are less common. A thorough examination is necessary to detect complications such as embolic events or metastatic infections.
Diagnosis requires prompt laboratory and imaging evaluation. Blood cultures are critical and should be obtained before starting antibiotics, with at least three sets drawn within the first 24 hours. Most cases can be diagnosed based on positive blood cultures. Laboratory findings often include leukocytosis, elevated inflammatory markers, and abnormalities on urinalysis such as hematuria or proteinuria. In cases of culture-negative endocarditis, serologic testing for atypical organisms may be necessary.
Echocardiography is the imaging modality of choice. Transthoracic echocardiography (TTE) is often used initially, but transesophageal echocardiography (TEE) is more sensitive and is preferred when clinical suspicion is high or when TTE results are inconclusive. Imaging may reveal vegetations, abscesses, or valvular dysfunction. Additional imaging studies may be required to evaluate for embolic complications or abscess formation in other organs.
Treatment involves prolonged intravenous bactericidal antibiotic therapy tailored to the causative organism and its antimicrobial susceptibilities. Empiric therapy is initiated based on clinical suspicion and risk factors. Common regimens include penicillin or ceftriaxone for streptococcal infections, ampicillin with gentamicin for enterococci, and nafcillin or vancomycin for Staphylococcus aureus. Therapy typically lasts several weeks to ensure eradication of infection within vegetations.
Surgical intervention is required in approximately 30–50% of cases and is considered in patients with heart failure, uncontrolled infection, large vegetations with recurrent emboli, or complications such as abscess formation. Management often requires a multidisciplinary approach involving cardiology, infectious diseases, and cardiac surgery teams.
Patients with endocarditis require hospitalization for initiation of treatment and close monitoring. Follow-up includes repeated blood cultures to confirm clearance of infection, monitoring for complications, and echocardiography to assess cardiac function after treatment. Patient education is important, particularly regarding oral hygiene and prevention of future infections.
The prognosis of NVIE depends on multiple factors, including the causative organism, patient comorbidities, and presence of complications. Mortality remains significant, with rates approaching 40% at one year. Poor prognostic factors include heart failure, infection with Staphylococcus aureus, older age, immunosuppression, and extension of infection beyond the valve. Complications include heart failure, stroke, systemic emboli, renal infarction, glomerulonephritis, mycotic aneurysms, and metastatic infections such as splenic abscess or meningitis.
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Infectious Disease And Microbiology – Encephalitis
Encephalitis is an inflammation of the brain parenchyma that leads to neurological dysfunction and is most commonly caused by infections. These infections may be viral, bacterial, fungal, or protozoal, with viruses being the most frequent cause. The condition typically arises when pathogens spread to the central nervous system via the bloodstream, although some, such as rabies, travel through peripheral nerves. Clinically, encephalitis often presents with fever, headache, confusion, and altered mental status, and may also involve seizures or focal neurological deficits.
Epidemiologically, encephalitis affects both extremes of age, particularly the very young and the elderly. Viral encephalitis is the most common form, with an annual incidence of approximately 3.5–7.4 cases per 100,000 people, accounting for around 20,000 new cases each year. In the United States, herpes simplex virus (HSV) is the leading identifiable cause, responsible for about 10% of all cases. In neonates, HSV-2 is the most common cause and is typically acquired during delivery. In many cases—up to 75%—no specific causative agent is identified.
Risk factors for encephalitis include age, immune status, seasonal exposure, and environmental or travel-related exposures. Arboviral infections are more common during summer and fall, while HSV infections occur year-round. Exposure to mosquitoes, ticks, animals, or contaminated water sources increases risk. Preventive strategies include avoiding insect bites, implementing vector control measures, and vaccination against preventable viral causes such as measles, mumps, rubella, polio, varicella, and Japanese encephalitis.
The pathophysiology varies depending on the causative organism but generally involves viremia followed by invasion of the central nervous system. This leads to inflammation, neuronal injury, and sometimes necrosis. In HSV encephalitis, the temporal lobes are commonly affected, whereas other viruses may target different brain regions such as the brainstem or gray matter.
Etiologically, encephalitis has a broad range of causes. Viral pathogens include herpesviruses (HSV, CMV, VZV), arboviruses (e.g., West Nile virus, Japanese encephalitis virus), enteroviruses, rabies virus, and HIV. Bacterial causes include Listeria monocytogenes, Mycobacterium tuberculosis, and Mycoplasma. Other causes include rickettsial organisms, spirochetes such as Borrelia burgdorferi, fungi like Cryptococcus neoformans, and protozoa such as Toxoplasma gondii and Naegleria fowleri. Helminths such as Taenia solium may also be implicated.
Diagnosis relies heavily on clinical suspicion, supported by history and examination. Important historical clues include recent travel, insect or animal exposure, and immune status. Physical examination focuses on neurological findings, though skin examination may reveal rashes that help identify specific etiologies. Because encephalitis may overlap clinically with meningitis, distinguishing between the two can be challenging.
Laboratory evaluation includes cerebrospinal fluid (CSF) analysis obtained via lumbar puncture, which typically shows lymphocytic pleocytosis, elevated protein, and normal glucose in viral cases. PCR testing of CSF is essential for identifying viral pathogens such as HSV, CMV, and VZV. Additional tests may include serology, blood cultures, and pathogen-specific assays depending on clinical suspicion. Imaging is critical, with brain MRI being the gold standard; characteristic findings such as temporal lobe involvement suggest HSV encephalitis. CT scanning is useful when MRI is unavailable or to rule out contraindications to lumbar puncture.
The differential diagnosis is broad and includes meningitis, brain abscess, encephalopathy, acute disseminated encephalomyelitis, metabolic disorders, vasculitis, and drug-induced aseptic meningitis. Management requires prompt empiric therapy. Until bacterial meningitis is excluded, patients should receive broad antimicrobial coverage along with antiviral therapy. Intravenous acyclovir is the treatment of choice for suspected HSV encephalitis and should be started immediately. Other antiviral or antimicrobial treatments depend on the identified pathogen, and adjunctive therapies such as antiretroviral treatment may be required in HIV-related cases.
Patients with encephalitis require hospitalization, often with intensive care monitoring. Supportive care includes adequate hydration, especially during acyclovir therapy to prevent renal toxicity. Close monitoring is essential, as recovery may be prolonged and incomplete.
The prognosis of encephalitis varies widely depending on the causative organism and timeliness of treatment. HSV encephalitis, if untreated, carries a mortality rate of up to 70%, but early treatment reduces mortality to 6–19%. However, many survivors experience long-term neurological deficits. Younger patients tend to have better outcomes.
Complications of encephalitis include seizures, permanent neurological impairment, relapse (particularly in HSV infection), and death. Long-term follow-up may involve neuropsychological assessment to evaluate cognitive and functional outcomes.
Encephalitis is an inflammation of the brain parenchyma that leads to neurological dysfunction and is most commonly caused by infections. These infections may be viral, bacterial, fungal, or protozoal, with viruses being the most frequent cause. The condition typically arises when pathogens spread to the central nervous system via the bloodstream, although some, such as rabies, travel through peripheral nerves. Clinically, encephalitis often presents with fever, headache, confusion, and altered mental status, and may also involve seizures or focal neurological deficits.
Epidemiologically, encephalitis affects both extremes of age, particularly the very young and the elderly. Viral encephalitis is the most common form, with an annual incidence of approximately 3.5–7.4 cases per 100,000 people, accounting for around 20,000 new cases each year. In the United States, herpes simplex virus (HSV) is the leading identifiable cause, responsible for about 10% of all cases. In neonates, HSV-2 is the most common cause and is typically acquired during delivery. In many cases—up to 75%—no specific causative agent is identified.
Risk factors for encephalitis include age, immune status, seasonal exposure, and environmental or travel-related exposures. Arboviral infections are more common during summer and fall, while HSV infections occur year-round. Exposure to mosquitoes, ticks, animals, or contaminated water sources increases risk. Preventive strategies include avoiding insect bites, implementing vector control measures, and vaccination against preventable viral causes such as measles, mumps, rubella, polio, varicella, and Japanese encephalitis.
The pathophysiology varies depending on the causative organism but generally involves viremia followed by invasion of the central nervous system. This leads to inflammation, neuronal injury, and sometimes necrosis. In HSV encephalitis, the temporal lobes are commonly affected, whereas other viruses may target different brain regions such as the brainstem or gray matter.
Etiologically, encephalitis has a broad range of causes. Viral pathogens include herpesviruses (HSV, CMV, VZV), arboviruses (e.g., West Nile virus, Japanese encephalitis virus), enteroviruses, rabies virus, and HIV. Bacterial causes include Listeria monocytogenes, Mycobacterium tuberculosis, and Mycoplasma. Other causes include rickettsial organisms, spirochetes such as Borrelia burgdorferi, fungi like Cryptococcus neoformans, and protozoa such as Toxoplasma gondii and Naegleria fowleri. Helminths such as Taenia solium may also be implicated.
Diagnosis relies heavily on clinical suspicion, supported by history and examination. Important historical clues include recent travel, insect or animal exposure, and immune status. Physical examination focuses on neurological findings, though skin examination may reveal rashes that help identify specific etiologies. Because encephalitis may overlap clinically with meningitis, distinguishing between the two can be challenging.
Laboratory evaluation includes cerebrospinal fluid (CSF) analysis obtained via lumbar puncture, which typically shows lymphocytic pleocytosis, elevated protein, and normal glucose in viral cases. PCR testing of CSF is essential for identifying viral pathogens such as HSV, CMV, and VZV. Additional tests may include serology, blood cultures, and pathogen-specific assays depending on clinical suspicion. Imaging is critical, with brain MRI being the gold standard; characteristic findings such as temporal lobe involvement suggest HSV encephalitis. CT scanning is useful when MRI is unavailable or to rule out contraindications to lumbar puncture.
The differential diagnosis is broad and includes meningitis, brain abscess, encephalopathy, acute disseminated encephalomyelitis, metabolic disorders, vasculitis, and drug-induced aseptic meningitis. Management requires prompt empiric therapy. Until bacterial meningitis is excluded, patients should receive broad antimicrobial coverage along with antiviral therapy. Intravenous acyclovir is the treatment of choice for suspected HSV encephalitis and should be started immediately. Other antiviral or antimicrobial treatments depend on the identified pathogen, and adjunctive therapies such as antiretroviral treatment may be required in HIV-related cases.
Patients with encephalitis require hospitalization, often with intensive care monitoring. Supportive care includes adequate hydration, especially during acyclovir therapy to prevent renal toxicity. Close monitoring is essential, as recovery may be prolonged and incomplete.
The prognosis of encephalitis varies widely depending on the causative organism and timeliness of treatment. HSV encephalitis, if untreated, carries a mortality rate of up to 70%, but early treatment reduces mortality to 6–19%. However, many survivors experience long-term neurological deficits. Younger patients tend to have better outcomes.
Complications of encephalitis include seizures, permanent neurological impairment, relapse (particularly in HSV infection), and death. Long-term follow-up may involve neuropsychological assessment to evaluate cognitive and functional outcomes.
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Infectious Disease And Microbiology – Empyema
Empyema is defined as the accumulation of purulent (pus-containing) fluid within the pleural cavity. It most commonly develops as a complication of bacterial pneumonia but may also arise following thoracic surgery, trauma, esophageal perforation, or subdiaphragmatic infections. In children, empyema is usually secondary to pneumonia—most often caused by Streptococcus pneumoniae—and tends to have a better prognosis than in adults, although management principles are similar. Overall, pleural effusions occur in up to 57% of pneumonia cases, but only about 1–2% progress to empyema. The condition affects individuals of all ages, with higher prevalence in the elderly and in children, and occurs more frequently in males.
Several risk factors predispose individuals to empyema, including diabetes mellitus, alcoholism, substance abuse, rheumatoid arthritis, chronic lung disease, poor dental hygiene, malignancy, and prior thoracic surgery. Conditions that increase the risk of aspiration are particularly associated with anaerobic infections. Prevention focuses on appropriate treatment of pneumonia, adherence to surgical infection control practices, and vaccination (especially pneumococcal vaccination).
The development of empyema progresses through three stages. The exudative stage involves inflammation and fluid accumulation in the pleural space. This is followed by the fibrinopurulent stage, characterized by fibrin deposition and pus formation. Finally, the organizing stage occurs, where fibroblasts proliferate and collagen is deposited, potentially leading to pleural thickening and restricted lung expansion. The causative organisms vary depending on whether the infection is community-acquired or hospital-acquired. Community-acquired empyema commonly involves streptococci, staphylococci, anaerobes, and Enterobacteriaceae, while hospital-acquired cases are more often caused by methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, enterococci, and other resistant organisms.
Clinically, patients often present with a history of pneumonia or thoracic procedures, along with symptoms such as fever, chest pain, and shortness of breath. In elderly or immunocompromised patients, symptoms may be subtle, including weight loss or anemia. On physical examination, findings may include dullness to percussion, decreased tactile fremitus, and absent breath sounds over the affected area, although small effusions may not produce obvious signs.
Diagnosis is confirmed through thoracentesis, with the presence of pus in the pleural space being definitive. Laboratory evaluation includes complete blood count and inflammatory markers such as C-reactive protein. Pleural fluid analysis is essential and typically shows low pH (<7.2), high white blood cell count, and positive Gram stain or culture. Imaging plays a key role: chest X-ray identifies pleural effusion, ultrasound helps localize fluid and guide drainage, and CT scan can distinguish empyema from lung abscess (notably showing the “split pleura” sign).
The differential diagnosis includes other causes of pleural effusion, lung abscess, and pneumonia. Management requires prompt initiation of antimicrobial therapy along with drainage of the infected fluid, usually via chest tube. Antibiotic regimens differ based on whether the infection is community- or hospital-acquired and should cover likely pathogens, including anaerobes and resistant organisms where appropriate. Adjunctive treatments include adequate hydration, nutritional support, and, in some cases, intrapleural fibrinolytic therapy to improve drainage.
In cases where drainage is incomplete or complications arise, surgical intervention may be necessary. Options include video-assisted thoracoscopic surgery (VATS), thoracotomy with decortication, or other open surgical procedures. Most patients require hospitalization for intravenous antibiotics and monitoring. Follow-up involves continued antibiotic therapy for 2–4 weeks, monitoring inflammatory markers, and ensuring adequate drainage. Chest tubes are typically removed once drainage decreases and fluid clears.
The prognosis of empyema varies depending on patient factors and timeliness of treatment. While many patients recover with appropriate management, mortality rates range from 7% to 33% within one year and may exceed 50% in patients with significant comorbidities. Complications include pleural thickening, pulmonary fibrosis, pneumothorax, bronchopleural fistula, respiratory failure, septic shock, and, in rare cases, empyema necessitatis.
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Infectious Disease and Microbiology – Ehrlichiosis and Anaplasmosis
Ehrlichiosis and anaplasmosis are systemic infections caused by obligate intracellular bacteria belonging to the family Anaplasmataceae, which includes the genera Ehrlichia, Anaplasma, Neorickettsia, and Wolbachia. These organisms primarily infect humans through tick bites, especially during the summer months when tick activity is highest. They target cells of the reticuloendothelial system, particularly monocytes and granulocytes, leading to a wide range of clinical manifestations. In immunocompetent individuals, the disease is often mild to moderate, presenting with nonspecific symptoms such as fever, malaise, headache, myalgias, nausea, and vomiting. However, in immunocompromised patients, including those with AIDS or on corticosteroid therapy, infections may become severe, with central nervous system involvement, multiple organ dysfunction, and even death.
Epidemiologically, ehrlichiosis and anaplasmosis are primarily reported in the United States but also occur worldwide. Human monocytic ehrlichiosis (HME), caused by Ehrlichia chaffeensis, is transmitted mainly by the tick Amblyomma americanum, particularly in the southeastern and south-central US. Human granulocytic anaplasmosis (HGA), caused by Anaplasma phagocytophilum, is transmitted by Ixodes scapularis, with most cases reported in regions such as Wisconsin, Minnesota, New England, New Jersey, and New York. Cases are also reported in parts of Europe. Subclinical infections are common, and many cases are underdiagnosed. Coinfections with other tick-borne pathogens, such as Babesia microti and Borrelia burgdorferi, may occur due to shared vectors.
Risk factors include exposure to tick-infested environments, outdoor activities in endemic areas, and immunosuppression. Prevention focuses on avoiding tick bites by wearing protective clothing, using insect repellents containing DEET, and performing thorough body checks after potential exposure. Prompt removal of ticks is essential to reduce transmission risk.
The pathophysiology involves bacterial invasion of host immune cells, where the organisms reside within membrane-bound vacuoles. Ehrlichia chaffeensis primarily infects macrophages, while Anaplasma phagocytophilum targets granulocytes. These infections lead to hematologic abnormalities such as leukopenia and thrombocytopenia, as well as systemic inflammation. If untreated, the disease can progress to severe multisystem involvement.
Clinically, symptoms usually develop about 7 days after a tick bite. Patients present with fever, malaise, headache, myalgias, nausea, and sometimes rash, which may be maculopapular or hemorrhagic. Lymphadenopathy and hepatosplenomegaly may occur. Severe cases can progress to septic shock, acute respiratory distress syndrome, and neurological complications such as seizures or coma. Human granulocytic anaplasmosis presents similarly but may lack rash unless there is coinfection with other tick-borne diseases.
Diagnosis is based on clinical suspicion supported by laboratory findings. Common laboratory abnormalities include leukopenia, thrombocytopenia, anemia, and elevated liver enzymes. Serologic testing using indirect immunofluorescence is considered the gold standard but may be negative early in the disease. Polymerase chain reaction (PCR) testing offers higher sensitivity during acute infection but requires specialized laboratories. Blood smear examination has low sensitivity. Imaging such as chest X-ray may show findings consistent with acute respiratory distress syndrome in severe cases.
The differential diagnosis includes other infectious and noninfectious conditions such as endocarditis, septicemia, vasculitis, thrombotic thrombocytopenic purpura, and other tick-borne illnesses including tularemia, babesiosis, Lyme disease, Rocky Mountain spotted fever, and murine typhus.
Treatment should be initiated promptly when the disease is suspected. Doxycycline is the first-line therapy and is effective for both ehrlichiosis and anaplasmosis, typically resulting in clinical improvement within 24–48 hours. Treatment duration is usually 7–14 days. In cases where doxycycline cannot be used, such as pregnancy, rifampin may be considered. Chloramphenicol has been used but is less reliable and may not be effective in all cases.
Follow-up is important to ensure clinical improvement, as lack of response within 48 hours should prompt reconsideration of the diagnosis. Persistent infection has been reported despite treatment, and expert consultation may be necessary in complicated cases.
Complications can be severe, particularly if untreated. These include respiratory failure, neurological involvement, acute renal failure, gastrointestinal hemorrhage, and death. Hospitalization is common, with a significant proportion of patients developing severe disease. Mortality rates are estimated at 2–5%, with higher risk in elderly and immunocompromised individuals.
