Primary HIV infection may go unnoticed in at least half of cases or produce a mild disease which quickly subsides, followed by a long clinical "latent" period lasting years. Prospective studies of acute HIV infections show that fever, lymphadenopathy, pharyngitis, diffuse erythematous rash, arthralgia/myalgia, diarrhea, and headache are the commonest symptoms seen with acute HIV infection. These symptoms diminish over 1 to 2 months. The symptoms of acute HIV infection resemble an infectious mononucleosis-like syndrome. Symptomatic acute HIV infection is more likely to occur in persons who acquired HIV infection through sexual transmission.
Generally, within 3 weeks to 3 months the immune response is accompanied by a simultaneous decline in HIV viremia. Both humoral and cell mediated immune responses play a role. The CD4 lymphocytes rebound in number, but not to pre-infection levels. Seroconversion with detectable HIV antibody by laboratory testing accompanies this immune response, sometimes in as little as a week, but more often in two to four weeks. Prolonged HIV-1 infection without evidence for seroconversion, however, is an extremely rare event.