text: Discussion
  We estimated the future acceptability of PrEP, examining the attitudes and preferences of potential user groups from different countries towards hypothetical and known PrEP attributes. Our results show that participants were generally willing to accept PrEP and adopt it as soon as it becomes available. Surprisingly, participants were also willing to take PrEP even when reminded of potential side effects, cost, condom use, and frequent HIV testing. These findings indicate participants' motivation to overcome barriers which can have a considerable impact on uptake. In contrast, participants mentioned that the thought of taking PrEP made them feel anxious, although they also indicated that taking PrEP would not be embarrassing and they would want their partner or partners to know. Participants' anxiety may be explained by the hypothetical nature of most of the presented PrEP characteristics, the stigma associated with HIV [34], and in some settings, the criminalization of sex work, injected drug use and homosexuality [35]. Most participants, nonetheless, subsequently indicated that PrEP would give them hope, which suggests that their initial willingness to take it remained largely unscathed.
  Female participants indicated a higher level of willingness to take PrEP than male participants, which may be explained by women's difficulty negotiating the use of condoms and awareness of their and/or their partners' risk of becoming infected with HIV [36]. We also found that younger participants and those with fewer children, those who reported adherence to past medication, more frequent condom usage, having been tested for HIV in the past and never injecting drugs, reported greater willingness to take PrEP. These promising findings suggest that those who are currently bearing the brunt of HIV [1], have higher perceived risk, and are most likely to adhere to a comprehensive PrEP program, are also the most motivated to enroll. Yet, while participants stated not being interested in selling PrEP, the majority reported intentions to share it. Therefore, information and counseling about the risks of sharing PrEP should be readily available as part of any implementation program.
  Results from the conjoint analysis reveal trends in participants' preferences which deserve consideration. PrEP route of administration was the most important attribute, and bi-monthly and monthly injections were the preferred alternatives. This finding is encouraging from a policy perspective if such modalities become available; since it may reduce users' likelihood of sharing, selling or forgetting to take PrEP, but it also raises questions regarding participants' willingness to take oral PrEP. HIV testing was the second most important attribute, and a test every six months was, as expected, the preferred alternative. Interestingly, dispensing sites were more important than any other attribute for some groups, particularly in Africa. This may indicate concerns about social stigma and access [37]. However, it is encouraging that most participants were willing to receive PrEP at a healthcare facility, which can facilitate synergies between PrEP and other existing prevention services. Time spent obtaining PrEP and frequency of pick up, which we used as a proxy measure for cost-opportunity, were generally less important, consistent with participants' willingness to pay for PrEP.
  Our findings are broadly consistent with the work of Guest et al. and Galea et al [18], [19]. However, specific comparisons are not advisable as the composition and size of the samples, recruitment methods, measures and statistical analyses differ greatly. Previous work on PrEP implementation suggests that delivery programs will need to meet a number of requirements in order to be effective, including: prioritization of groups at higher risk of infection; delivery of PrEP in combination with other prevention services, including risk reduction and medication adherence counseling, condoms provision, diagnosis and treatment of other sexually transmitted infections, and frequent HIV testing; and monitoring of side effects, adherence and risk behaviors [8], [38], [39], [40], [41], [42]. Our results provide valuable clues that can help countries to deliver PrEP more effectively, should they decide to implement it, by focusing their efforts on the aspects that need more attention.
  This is the first multinational study, to our knowledge, that integrates different disciplines to shed light on a question that we believe is of global importance. Our study complements previous work on PrEP by examining potential users' perspective and offering insights into their attitudes and preferences. We note that it may not be possible to generalize the observed PrEP acceptability to other settings and our results should be considered within the context of this study's limitations. Given the sensitive nature of the addressed questions, and despite all our efforts to reduce social desirability bias, there is an unavoidable risk that participants may have felt at times compelled to provide what they felt was the "right" answer. Additionally, our data collection took place in urban areas, where HIV incidence is normally higher, thus current findings may not be generalizable to rural settings. Finally, examining acceptability among users enrolled in pilot programs is much deserving, as actual acceptability may differ from potential willingness to take PrEP, especially if relevant attributes of a product or program are modified, as observed in other comparable interventions [43].
  
  