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KembaraXtra-Emergency and Acute Medicine - Opportunistic Infections
Description: Opportunistic infections are unusual infections that occur when host defenses are impaired, allowing normally nonpathogenic organisms to cause disease. They are most commonly associated with advanced immunosuppression and may present with subtle or atypical signs, yet progress rapidly to severe systemic illness.
Etiology: In patients with HIV/AIDS, opportunistic infections typically occur when the CD4 T-lymphocyte count falls below 200 cells/mm³ or <14% of total lymphocytes. common pathogens include pneumocystis jiroveci (pcp), disseminated tuberculosis, toxoplasma gondii, cryptococcus, histoplasma, cytomegalovirus, mycobacterium avium complex, jc virus (progressive multifocal leukoencephalopathy), hepatitis b virus, and human herpesvirus-8 (kaposi sarcoma). cell-mediated immune deficiency from hematologic malignancies, lymphoma, high-dose glucocorticoids, autoimmune disease, chemotherapy, radiation, or viral infections predisposes to such as legionella, nocardia, salmonella, mycobacteria. neutrophil impairment depletion due cytotoxic drugs, aplastic anemia, marrow infiltration, drug reactions, vitamin deficiencies increases risk for with staphylococcus, α-hemolytic streptococcus, enteric organisms, anaerobes, invasive aspergillosis.< />pan>
Clinical features: Patients may present with new or worsening fatigue, fever or hypothermia, chills, night sweats, tachypnea, and signs of systemic inflammatory response. Pulmonary sources cause cough, dyspnea, and rales; genitourinary sources cause dysuria, frequency, or retention; gastrointestinal sources cause abdominal pain, vomiting, diarrhea, bleeding, or jaundice; and CNS involvement may cause confusion, headache, focal neurologic deficits, or seizures. Ambulatory hypoxia is characteristic of PCP pneumonia, and oropharyngeal candidiasis is a key marker of immune suppression.
Evaluation: A thorough history is essential, including known HIV status and CD4 count, malignancy or transplant history, autoimmune disease, and use of cytotoxic or high-dose steroid therapy. Physical examination must be comprehensive, as classic signs of infection may be minimal or absent. Fever or any clinical deterioration should prompt full evaluation.
Diagnostic testing: Laboratory evaluation includes CBC with differential to identify leukocytosis or neutropenia, calculation of absolute neutrophil count, blood and site-specific cultures, urinalysis, electrolytes, renal function, glucose, lactate, coagulation studies, and LDH (often elevated in PCP). If CD4 count is unknown, an absolute lymphocyte count <1,000 />mu;L predicts CD4 <200. imaging includes chest radiography, which may show nonspecific infiltrates or bilateral interstitial changes in pcp, and high-resolution ct of the for early pcp detection. head with contrast is indicated focal neurologic deficits suspected toxoplasmosis, abdominal pelvic warranted when a gastrointestinal source suspected. lumbar puncture required cns infection suspected, diagnostic paracentesis should be performed immunocompromised patients ascites.< />pan>
Management: Initial stabilization focuses on airway, breathing, and circulation, with supplemental oxygen, IV access, fluid resuscitation for hypotension, cardiac monitoring, and early empiric antimicrobial therapy. Broad-spectrum antibiotics are initiated promptly, often using antipseudomonal penicillins with aminoglycosides or monotherapy with third- or fourth-generation cephalosporins, fluoroquinolones, or carbapenems when indicated. Vancomycin is added in areas with high prevalence of resistant organisms. Antifungal therapy is initiated if there is no improvement after adequate antibacterial coverage, and trimethoprim–sulfamethoxazole is first-line therapy for suspected PCP, with alternatives for intolerance. Corticosteroids are indicated in PCP with hypoxemia and should be started within 72 hours of antimicrobial therapy.
Disposition and follow-up: All patients with suspected or confirmed systemic opportunistic infections require hospital admission. Discharge is appropriate only when systemic infection has been confidently excluded. Infectious disease consultation is strongly recommended. Clinicians must maintain a high index of suspicion, as immunocompromised patients may present with minimal signs yet deteriorate rapidly.
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