Which opportunistic infections require routine prophylaxis in HIV patients?

• A. Prophylaxis is based on CD4 > 500.
• B. No prophylaxis is needed.
• C. PJP prophylaxis with TMP-SMX when CD4 < 100; toxoplasma prophylaxis with TMP-SMX when CD4 < 100; MAC prophylaxis with azithro/clarithro when CD4 < 50.
• D. Prophylaxis for MAC when CD4 < 100.

Answer: (C)

The key idea is that HIV patients are protected against certain infections only when their immune system is strong enough, so we use CD4 counts to decide when to start prophylaxis. The infections most routinely prevented with prophylaxis are Pneumocystis jirovecii pneumonia (PJP), toxoplasma encephalitis, and Mycobacterium avium complex (MAC). TMP-SMX is used to prevent both PJP and toxoplasma when the CD4 count is at levels where risk rises, while MAC prophylaxis uses a macrolide like azithromycin or clarithromycin when the CD4 count is very low. The option listing these three prophylactic strategies at their respective CD4 thresholds captures the standard pattern of routine prophylaxis, which is why it is the best answer. In practice, the PJP prophylaxis threshold is commonly cited as when CD4 counts fall below 200 cells/µL, toxoplasma prophylaxis below 100, and MAC below 50, with adjustments based on serostatus and ART response.