https://www.poz.com/article/prep-fails-gay-man-adhering-daily-truvada-contracts-drugresistant-hiv
http://instinctmagazine.com/post/canadian-prep-user-contracts-strain-prep-resistant-hiv
Combining PrEP with condoms is the safest way to go. STI's aside, there've also been a few times an escort wasn't exactly clean and sparking down there, if you know what I mean, and I was glad I had a condom on.