What is the daily prophylactic treatment for patients with HIV and a CD4 count less than 200 cells/mm³?

In patients with HIV who have a CD4 count of less than 200 cells/mm³, there is an increased risk for opportunistic infections, particularly Pneumocystis jirovecii pneumonia (PCP). The recommended prophylactic treatment to reduce the risk of PCP in these patients is daily trimethoprim-sulfamethoxazole. This antibiotic not only has activity against Pneumocystis jirovecii but also against several other pathogens, making it a robust choice for prophylaxis in this population.

The other options do not serve the same purpose in this context. While azithromycin is used for other infections such as mycobacterial infections, it is not specifically used for PCP prophylaxis. Fluconazole is primarily used for fungal infections such as cryptococcal meningitis but isn't indicated for PCP prophylaxis. Lastly, while the pneumococcal vaccine is important for preventing pneumococcal disease, it does not serve as a daily prophylactic treatment and is not a substitute for medication aimed at pneumocystis prevention. Hence, daily trimethoprim-sulfamethoxazole remains the standard recommended prophylactic treatment for patients with low CD4 counts at risk for PCP.