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Background: Some have expressed concern that gay and bisexual men (GBM) who use pre-exposure prophylaxis (PrEP) will engage in more condomless anal sex (CAS) and acquire/transmit STIs more frequently while on PrEP. Others, however, argue that increases in STIs among men on PrEP result from required STI screening and testing. There has been little longitudinal data to support either conclusion.
Methods: Data were collected from One Thousand Strong, a longitudinal study of 1,071 HIV-negative GBM from across the U.S. Participants were tested for urethral and rectal gonorrhea and chlamydia and asked to report on their PrEP use every 12 months.
Results: In cross-sectional between-group analyses, the 823 PrEP-naïve men had a significantly lower STI infection rate (4.2%) than the 77 men currently (10.4%) or 17 men formerly (11.8%) on PrEP, X2(2) = 7.72, p = 0.02; men currently on PrEP also reported significantly more acts of CAS, H(2) = 37.73, p < 0.001. Within-person longitudinal analyses of the 181 men who reported PrEP use indicated slight but non-significant increases in the odds of an STI diagnosis while on PrEP (OR = 1.25, p = 0.55) and after discontinuing PrEP (OR = 1.43, p = 0.53) in comparison to pre-uptake of PrEP. We also saw no significant changes in CAS while on PrEP (OR = 1.09, p = 0.76) or after PrEP discontinuation (OR = 0.48, p = 0.10) compared to pre-uptake levels.
Conclusions: Our findings failed to support the notion that GBM experience an increase in CAS and STIs while on PrEP. Although PrEP-naïve GBM have fewer STIs and report less CAS than current and former PrEP users, these data provide support for the notion that the highest risk GBM are the ones who initiate PrEP use, and their risk behaviors do not change substantially as a result. It is worth noting that most of the men on PrEP in this sample are early adopters, and further research is needed to determine whether behavioral differences may emerge in larger samples of men who may engaging in lower levels of HIV risk behavior at the time of PrEP initiation.

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