Seroconversion is the period between exposure to a virus and when antibodies show up in the blood. In the case of HIV, seroconversion is the time from HIV exposure to infection and to developing antibodies that can be detected by a test. This period can take a few weeks and is sometimes called the window period. During seroconversion, the body starts producing detectable levels of HIV antibodies, and most HIV tests check for the presence of these antibodies. The majority of infected individuals experience seroconversion within three weeks, and antibodies appear within one to two weeks and will continue to increase in the months after infection.

Seroconversion is often, but not always, accompanied by a flu-like illness, which happens in at least half of the people infected with HIV, but may happen in as many as 80-90% of all infections. The most common symptoms of seroconversion include fever, swollen glands, muscle aches, and tiredness. Other symptoms may include body rash, oral thrush, weight loss, joint pains, sore throat, gastrointestinal symptoms, headache, genital sores or thrush, night sweats, and nervous system involvement. However, these symptoms are not a reliable way to identify seroconversion, to diagnose HIV infection, or to rule it out, as they can be similar to symptoms of other illnesses.

It is important to note that a person can transmit HIV before seroconversion, and even when the immune system has not yet produced detectable amounts of HIV antibodies, the virus is still active. Therefore, anyone concerned about HIV exposure should speak to a healthcare provider and get tested. The only way to confirm HIV infection is through an HIV test, which needs to be done after the window period.