I have had unprotected sex with someone I now believe to be HIV-positive and the day after I had unprotected sex with an ex-girlfriend. I tested myself the day after I had sex with my ex-girlfriend and the test has shown up negative. I do know it can take a long time for HIV to show up on a test. But I need to know: Is there a possibility I infected my ex-girlfriend with HIV even though I tested negative the day after?
Thank you for your inquiry. From what we gather from the question, you were asking about the risk of acquiring and transmitting HIV from unprotected vaginal sex. From the information given, this scenario is determined to be of High Risk (There is evidence of transmission through these activities and are the majority of cases of transmission).
HIV transmission occurs when bodily fluid containing HIV has direct access to the bloodstream of an individual through a high risk activity. The scenario mentioned above does meet the three components of the Transmission Equation because unprotected vaginal sex is an activity that allows direct access of potential HIV-containing fluids (eg. vaginal fluids or menstrual blood) to the bloodstream (eg. through your urethra). The risk assessment is based solely off of the unprotected vaginal sex mentioned in the scenario.
Depending on the test that was employed, each test will look for different components in the blood to assess the potential for a positive result. Some will look for antibody production (3rd generation, and 4th generation Enzyme immunoassay (EIA)) and some will look for viral RNA in the blood before antibodies have been formed, which may confirm a positive HIV status earlier than the other tests. However, these tests are not completely conclusive until the respective window periods are met. The earliest window period is the Pooled RNA NAAT Aka - "early test", which has a 90% accuracy rate after 10 - 12 days, and a 95% accuracy after 6 weeks. Thus, testing the next day does not give a reliable source of reasonable doubt. During and before the window period, a person can transmit HIV but still test HIV negative. If you are continuously engaging in High Risk activity there are biomedical approaches such as PrEP and PEP that may help lower your risk of acquiring HIV. Refer to your physician for further information.
You may also want to consider having an open and honest discussion with your ex-partner. They can then have the opportunity to ask their healthcare providers to explain viral load and the risks of HIV transmission.
Recommendation: Refer to a physician for an HIV test outside of the window period (6 weeks and 3 months post-exposure for completely conclusive results).
AIDS Vancouver Helpline/Online, Jason