HIV/AIDS Basics

Human immunodeficiency virus infects and progressively destroys CD4-positive T lymphocytes. These cells coordinate cellular immune responses, so their loss leaves the patient less able to contain organisms that a healthy immune system would usually control. The result is not simply “more infections”; it is a changing pattern of infections, malignancies, weight loss, and organ complications as immune function declines. Acute HIV infection may occur 2 to 4 weeks after exposure and can resemble influenza or mononucleosis: fever, rash, sore throat, lymphadenopathy, myalgias, headache, or diarrhea. These findings are nonspecific, so a recent exposure matters. A negative antibody-only rapid test does not reliably exclude early infection because antibodies may not yet be detectable. AIDS describes advanced HIV infection, generally marked by a CD4 count below 200 cells/µL or an AIDS-defining condition. Pneumocystis jirovecii pneumonia is a classic opportunistic infection at this level of immune suppression. Cryptococcal meningitis is another dangerous possibility, particularly when headache, fever, confusion, or neck stiffness develops. Effective ART can suppress viral replication, preserve or restore CD4 function, and prevent progression.