Preexposure prophylaxis (PrEP) with oral tenofovir disoproxil fumarate and emtricitabine (TDF-FTC or Truvada) has been demonstrated to be highly effective at preventing HIV infection in high-risk MSM in three landmark studies [1–3]. In the United States, the Food and Drug Agency approved the use of PrEP in July 2012  and PrEP is now reimbursed through the Medicaid program and the majority of private insurers. PrEP is offered through a patchwork of schemes in the United States, and has been pioneered in a number of clinics in the San Francisco Bay Area [5,6]. PrEP was approved by Health Canada in February 2016 as part of a comprehensive HIV Prevention strategy [7,8]. In Quebec, TDF-FTC has been covered as a general benefit of the provincial healthcare coverage since 2007, without restriction to use as PrEP .
Concerns have been raised that PrEP use may be accompanied by the phenomena of risk compensation or behavioural disinhibition, whereby PrEP users’ perception of decreased risk of HIV acquisition may lead them to engage in overall riskier sexual practices and increase their chances of acquiring sexually transmitted infections (STIs) . Modifiable behaviours which may impact transmission of STIs include: condom use, number of partners, concurrency or gaps between partners, partner characteristics, and healthcare-seeking behaviours . Additionally, MSM may alter HIV risk mitigation practices while on PrEP by decreasing seroadaptive practices such as seeking a partner of similar perceived serostatus (e.g. serosorting), or the use of strategic positioning whenever engaging in anal sex with a partner of known HIV positive status (seropositioning) . Among PrEP users, high rates of STIs have been reported [13–15], as well as high rates of condomless sex , and increasing rates of STIs over time . However, data from the US National HIV Behavioural Surveillance surveys have documented secular trends of decreasing rates of condom use prior to PrEP, with the percentage of men with no condomless anal sex partners decreasing from 61% in 2001, to 54% in 2011 and 40% in 2014 .
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