Man on PrEP tests HIV postive - Highly resistant strain of HIV

I guess it's the same with any sort of safe sex, that nothing is 100% effective. Condoms can break for example. In this case although the man was taking Truvada correctly as prescribed, and despite the proven effectiveness of PrEP to stop HIV infection, he has tested positive to the virus. 

The reason? A highly resistant strain of HIV:

Researchers have for the first time documented a case of an individual contracting HIV, a multi-drug resistant strain, while apparently adhering well to the daily regimen of Truvada (tenofovir/emtricitabine) as pre-exposure prophylaxis (PrEP). The scientists concluded that it is indeed possible for individuals who are adherent to PrEP to contract HIV when they are exposed to a virus that is resistant to both drugs included in Truvada. 

While this case is concerning, experts in the PrEP field believe that such failures of PrEP will likely remain rare. 

David Knox, MD, an HIV specialist at the Maple Leaf Medical Clinic and the lead author of the case study, presented findings at the 2016 Conference on Retroviruses and Opportunistic Infections (CROI) in Boston. 

Evidence suggests that the individual in question, a 43-year-old man who has sex with men, adhered well to PrEP over the long-term. Nevertheless, after 24 months on Truvada he tested positive for HIV. Initial tests indicated that he was acutely (very recently) infected: He tested positive for the p24 antigen, which appears within about three weeks of HIV infection and disappears a few weeks afterward; and at that time he tested negative for HIV antibodies, which typically appear two to eight weeks after infection. 

Researchers estimate that men who have sex with men (MSM) who take Truvada at least four times a week are more than 99 percent protected against HIV. (CDC guidelines advise taking Truvada daily for maximum protection, but the drug apparently has a good amount of dosing “forgiveness.”) Real-world use of Truvada as HIV prevention has suggested it is indeed highly effective. For example, none of the more than 1,400 generally high-risk individuals taking PrEP through the Kaiser Permanente San Francisco PrEP program have contracted HIV to date, despite their very high rate of other sexually transmitted infections, including two cases of hepatitis C virus (HCV) . 

All of PrEP’s power to curb HIV notwithstanding, this new case study underlines the fact that in science there is, unfortunately, no 100 percent guarantee. POZ