Acute primary HIV infection.

Third-generation enzyme immunoassays start to de tect anti-HIV antibodies within 20–22 days after exposure; fourthgeneration enzyme immunoassays, which test for p24 antigen and anti-HIV antibodies, can yield positive re sults within 16–18 days. RNA nucleic acid amplification testing starts to de tect HIV infection within 7–14 days. At $75 per test, these RNA tests are too costly for routine use and are typically reserved to detect pre-seroconversion infection in at-risk prenatal women and to rule out neonatal infection. Most patients who know they have acute HIV infection will change their behaviour