Thailand has been a global leader in the response to the HIV epidemic in behavioral prevention, microbicides, and in the conduct of pivotal efficacy trials of preventive vaccine candidates.(9–11) However, the bulk of these studies are conducted based on incidence information gathered in larger urban centers such as Bangkok and Chiang Mai, where the epidemic is concentrated. Updated information on HIV incidence is necessary to monitor and respond to the HIV epidemic both within and outside of large urban centers. This study contributes HIV incidence information for two provinces outside of Bangkok, Ratchaburi and Nakorn Ratchasima. These sites were chosen based on activities around commercial sex work and provincial hospitals having an established history in working with community-based organizations serving key populations at risk for HIV. These community—based organizations played a key role in recruitment and retention of participants.
HIV incidence was similar at both sites, with an incidence rate in Ratchaburi of 1.58 per 100 PY and in Nakorn Ratchasima of 1.57 per 100 PY, both lower than previously reported among young MSM in Bangkok (7.4 per 100 PY).(2, 4, 12, 13) While these studies have identified young MSM at highest risk for HIV, we did not observe any statistically significant differences in HIV seroconversion by age. However, this cohort was very young overall, with a median age of 22 years.
Although PrEP knowledge and usage was very low at the beginning of the study, over half said they would be interested in taking PrEP. However, only four participants initiated PrEP during the study despite one site having PrEP demonstration projects available. Thus, barriers to access were not the sole factor in choosing not to initiate PrEP. Similarly, less than a third of participants had ever received information about vaccine research; however, 82% reported being willing to participate in a future HIV vaccine trial. This finding is promising and could indicate high levels of PrEP uptake should it become widely accessible and vaccine uptake should an HIV vaccine become widely available. This study could be useful as a baseline HIV incidence assessment that will benchmark falling incidence rates as PrEP is implemented more widely in these regions. Consistent with prior studies, low self-perceived risk was a key barrier to PrEP interest and will need to be addressed to optimize deployment of PrEP or an effective HIV vaccine.(14) Taken together, it is clear that focused and early prevention efforts and engagement with young MSM and TGW remain critical to curbing HIV transmission in these populations, and that these efforts can be further expanded outside of the major urban centers.
Consistent with other literature, receptive anal intercourse was significantly and independently associated with incident HIV-infection. The risk of HIV transmission via anal intercourse has been well described, though may be modified by frequency of sex acts, ART use and viral load of a partner living with HIV.(15) It should be noted that this study enrolled only individuals engaging in anal sex; however, although anal sex of any type was a criterion for inclusion, those engaging in receptive anal sex were found to be at increased risk for HIV seroconversion as compared to those not engaging in receptive anal sex. Recent STI diagnosis was associated with HIV seroconversion and may indicate shared behavioral factors that contribute to HIV and other STI acquisition. Evidence from studies conducted in other settings suggests that STIs, particularly rectal STIs, may increase the risk of HIV acquisition through biologically mediated pathways.(16–18) This finding provides support for screening and treatment of STIs as part of a comprehensive package for HIV prevention.
Sex with a sex worker was found to be associated with a lower risk of HIV seroconversion after adjustment. Other studies have observed high levels of consistent condom use among female sex workers, particularly with nonregular partners.(19) Additionally, a pooled analysis of Demographic and Health Survey data from 29 sub-Saharan African countries found that consistent condom use among men paying for sex was overall high, 84.0% (CI: 80.4–87.6), but varied by demographic characteristics.(20) High levels of condom use with sex workers may help to partially explain this unanticipated finding; however, additional research is needed to further explore this association in this setting.
Although we did not find a significant relationship between condom use at last sex and HIV seroconversion, this may be due to several factors. Condom use at the last prior sexual exposure may not be an accurate representation of risk, especially in those individuals with frequent sexual risk behavior. Given that behavioral data was based on self-report, data could potentially be influenced by social desirability or recall bias. Additionally, robust associations may have been difficult to detect due to relatively small number of HIV seroconversion events. Finally, individuals enrolled and retained in a longitudinal cohort may be more motivated to engage in health promoting and HIV prevention activities and less inclined to engage in risky behaviors, potentially limiting the generalizability of our finding to other populations of MSM and TGW.