Which infection is most commonly associated with HIV as an opportunistic infection?

• A. Pneumocystis jiroveci
• B. Cytomegalovirus
• C. Mycobacterium tuberculosis
• D. Candida albicans

Answer: (A)

Opportunistic infections in HIV are defined by infections that take advantage of severe immune suppression, especially when CD4 counts fall below about 200 cells per microliter. The classic, most common opportunistic pneumonia in AIDS is Pneumocystis jirovecii pneumonia. It often begins with a subacute fever, dry cough, and progressive shortness of breath, and chest imaging typically shows diffuse bilateral interstitial infiltrates. Diagnosis is made by identifying Pneumocystis jirovecii in respiratory specimens using special staining or PCR from induced sputum or bronchoalveolar lavage. Because of its strong association with advanced HIV infection, PCP is a hallmark opportunistic infection and a key reason for initiating prophylaxis with trimethoprim-sulfamethoxazole when CD4 counts are low. The other infections listed can occur in HIV, but they do not define the most common opportunistic pneumonia in this setting: CMV causes other organ-specific diseases (like retinitis), TB is common but not the prototypical opportunistic pneumonia, and Candida often presents as thrush or esophagitis rather than the defining opportunistic pneumonia.