During primary HIV infection, seroconversion occurs -- the appearance of detectable antibodies to HIV in the blood. It normally takes several weeks to several months for antibodies to the virus to develop after HIV transmission. When antibodies to HIV appear in the blood, a person will test positive in the standard ELISA test for HIV.
Primary HIV infection may or may not include acute HIV, a flu-like syndrome that occurs immediately after a person contracts HIV. Acute HIV is characterized by fever, sore throat, headache, skin rash and swollen glands (lymphadenopathy).