It has come to my attention that there is some confusion regarding HIV testing and the transmissibility of HIV. A brief summary is as follows. Upon initial infection, the virus rapidly replicates inside the host and is immediately contagious. Unfortunately, modern testing can not detect the virus for a period of time, known as a window period. During the initial period of infection, the person has an undetectable viral load but is still infected. This is a false negative test result. A NAT test can become positive around 10 days while the antigen/antibody test takes about 18 days. During this acute infection period, the individual is highly contagious with rapidly replicating virus. During the initial infection, undetectable means a window period exists and the virus is most definitely transmittable.
If a patient begins treatment with ART, the viral load may become undetectable. The virus is being suppressed but is still inside the body and can increase in number if the medication is stopped. Additionally, viral blips may occur when the viral load increases for unknown reasons and then becomes undetectable again. If a person is on ART consistently and has an undetectable viral load for 6 months by repeat blood tests; only then is the virus thought to be non transmittable. The person needs to be compliant and consistent with the medication. Having a negative test is only accurate to the day the blood is drawn. If a patient is infected the next day then the previous test is meaningless.
Furthermore, once infected with HIV, the antibody test will always be positive and there will always be a risk of spreading infection if not properly treated. To be crystal clear, undetectable in the window period is a false negative test and contagious. Undetectable only means non transmittable if the person is consistently on effective medications. Knowing yours and your partners status is critical to proper prevention strategies.