Risk and severity of opportunistic infections, AIDS, and AIDS-related cancers are determined by 2 factors: CD4 count Exposure to potentially opportunistic pathogens Risk of specific opportunistic infections increases below threshold CD4 counts of about 200 / mcL for some infections and 50 / mcL for others, as in the following: CD4 count < 200 / mcL: Increased risk of Pneumocystis jiroveciipneumonia, toxoplasmic encephalitis, and cryptococcal meningitis CD4 count < 50 / mcL: Increased risk of cytomegalovirus (CMV) and Mycobacterium avium complex (MAC) infections For every 3-fold (0.5 log 10) increase in plasma HIV RNA in untreated patients, risk of progression to AIDS or death over the next 2 to 3 years increases about 50% (6).