It is important to make sure you have not been recently infected with HIV when starting PrEP. Truvada is not designed to be used on its own to treat HIV, so using Truvada PrEP if you already have HIV means you are not getting optimal treatment to suppress the virus; you may be increasing your risk of developing drug resistance and limiting your future options for HIV treatment. If you are recently infected with HIV, there is a “window period” when traditional HIV antibody tests cannot yet detect the virus. When you ask about starting PrEP, your medical provider or study coordinator may suggest an alternative test that can detect HIV infection earlier.