A patient who has a history of HIV presents to the clinic for a routine follow-up. The NP should recognize that this patient is at the highest risk for which of the following infections when their CD4 count is 500 cells/microliter?

A CD4 count of 500 cells per microliter is within the normal to near-normal range, as a healthy adult typically has a CD4 count between 500 and 1,500 cells per microliter. At this level of immune function, the patient is at highest risk for opportunistic infections that can occur even at relatively preserved immunity. Tuberculosis is notable because Mycobacterium tuberculosis is highly virulent and can cause active disease in HIV-infected individuals even when CD4 counts are above 500 cells per microliter; in fact, TB is considered an AIDS-defining illness that can emerge at any CD4 level, but it is particularly relevant at higher counts compared to other opportunistic infections. Pneumocystis jirovecii pneumonia prophylaxis is generally recommended when CD4 counts fall below 200 cells per microliter, so at 500 cells per microliter the risk is relatively low. Histoplasmosis dissemination typically occurs when CD4 counts drop below 150 cells per microliter. Cryptococcal meningitis is most common at CD4 counts below 100 cells per microliter. Because tuberculosis poses significant risk even at higher CD4 counts unlike the other listed organisms, which require more profound immunosuppression, tuberculosis is the correct answer for a CD4 count of 500 cells per microliter.