A 42-year-old woman with HIV (CD4 count 25 cells/μL, defaulting follow-up) presents with 6 weeks of intermittent fever, night sweats, weight loss, and abdominal discomfort. Examination shows hepatosplenomegaly. Blood cultures grow acid-fast bacilli later identified as Mycobacterium avium complex. At what CD4 threshold should primary prophylaxis against this organism have been started?

• A Below 50 cells/μL ✓
• B Below 150 cells/μL
• C Below 100 cells/μL
• D Below 200 cells/μL

Explanation

Disseminated MAC disease occurs almost exclusively when the CD4 count is below 50 cells/μL, and guidelines recommend azithromycin or clarithromycin weekly prophylaxis at this threshold, after ruling out active tuberculosis. The other thresholds correspond to different interventions: below 200 for Pneumocystis prophylaxis and below 100 for toxoplasmosis prophylaxis. Prophylaxis can be discontinued once ART restores the CD4 count above 100 cells/μL for at least 3 months.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.