Which Mycobacterium species is most commonly associated with disseminated disease in HIV/AIDS patients?

• A. M. avium complex
• B. M. kansasii
• C. M. gordonae
• D. M. marinum

Answer: (A)

Disseminated disease in advanced HIV/AIDS is most commonly caused by the Mycobacterium avium complex. This group, including M. avium and related species, has a strong tendency to spread hematogenously in severely immunocompromised hosts, leading to fever, night sweats, weight loss, anemia, and hepatosplenomegaly with positive blood or bone marrow cultures. The risk rises when CD4 counts fall below about 50 cells/µL, making MAC the classic opportunistic infection in this setting. Clinically, patients may have high alkaline phosphatase and cytopenias due to widespread infection.

Other mycobacteria listed have different typical presentations. M. kansasii more commonly causes pulmonary disease resembling TB rather than disseminated illness in AIDS. M. gordonae is frequently a nonpathogenic contaminant or causes disease only rarely. M. marinum produces localized skin and soft tissue infections, usually from aquarium exposures, and does not typically disseminate.

So, the best answer is the Mycobacterium avium complex because of its predilection for disseminated infection in severely CD4-depleted patients.