Hello. Thanks for writing to us at healthcaremagic Unprotected sex is a high risk for all types of STD s, specially if it was with a person of unknown sexual status. Almost all the STD s like herpes, syphilis, gonorrhea, warts, molluscum and HIV are transmitted through unprotected sexual acts. I think you took a screening test for HIV. Screening for HIV can be done earliest at 4 weeks to be considered reliable because most of those who are infected with HIV go on to develop antibodies within a month. I think you took up the screening test a bit too early and therefore, I suggest you to repeat it at 1 month. The chances of acquiring HIV by a male from a single unprotected peno-vaginal sexual exposure are about 1 in 2500. Therefore though the chances are pity less but having said that a single exposure can result in infection. Apart from HIV you must also get tested for other STD s like gonorrhea, chlamydia, herpes, syphilis by blood tests at appropriate intervals. Testing at 2 weeks for herpes and at 1 month for syphilis and HIV is advisable. HIV and syphilis should be tested again at 3 months if testing at 1 month is negative. Moreover, if you notice any growth or ulcer or urethral discharge, you should immediately contact your doctor for the needful. Take care regards Always practice safe sex with a condom!