Acute HIV diagnostic timeline. Symptoms, when present, typically occur around 2 weeks after infection. Viremia is detectable prior to symptoms in the form of HIV p24 antigen (detectable by ELISA) or HIV RNA (detectable by even more sensitive nucleic acid amplification). While viremia reaches extremely high levels in the month or two following infection, p24 antigen typically becomes undetectable shortly before seroconversion, because of the formation of early antibody-antigen complexes. A secondary antibody-negative, p24 antigen–negative period is sometimes observed.