Pre-exposure prophylaxis (PrEP) has gained a central role in prevention of HIV infection amongst men who have sex with men (MSM) and has been vigorously promoted in San Francisco, California, USA. Our city was an early site for research and the first clinical trial for PrEP [1], open label continuation [2], and now engaged in expanding PrEP offering through private [3] and public PrEP clinics [2, 4]. The safety and efficacy of the preventative medication have been demonstrated in clinical trials, especially amongst MSM [1, 5, 6]. Other research has demonstrated the acceptability and demand for PrEP amongst MSM [7–10]. Less is known about the extent of use of PrEP amongst MSM outside the context of trials, demonstration projects and clinics. In particular, data need to track the use of PrEP in population- or community- based surveys to gauge eligibility and use and to identify disparities in access.

Guidance on which MSM should be recommended PrEP use has been formulated by the Centers for Disease Control and Prevention (CDC) [11]. Recommendations for PrEP use in HIV-negative MSM are: a) has an HIV-infected partner, or b) is not in a mutually monogamous relationship with an HIV-uninfected partner, and c) has condomless anal intercourse or had a sexually transmitted infection (STI) in the past six months. These CDC guidelines do not consider factors such as age and race/ethnicity, which are associated with greater rates of HIV transmission amongst MSM in the US [12].

A better understanding of who is taking up PrEP (vis-à-vis recommended criteria and demographic characteristics) is essential to provide information enabling public health officials and clinicians to better prioritise segments of populations in need of PrEP. Such foundational information will inform current and future efforts to stabilise HIV incidence and close persistent disparities. As an early epicenter of the HIV epidemic amongst MSM and given the vigorous scale-up of PrEP, San Francisco’s experience may presage trends elsewhere. We therefore undertook the present analysis to describe PrEP uptake in a community-based sample of MSM in San Francisco.

San Francisco’s 2014 implementation of NHBS MSM recruited 411 MSM. Of those, 301 (73.2 %) self-reported being HIV-negative (Table 1). A majority was between 25 and 44 years old (60.5 %), White (54.8 %), had at least some college education (86.4 %), or earned $50,000 USD per year or greater (53.4 %). Fully 87.7 % of HIV-negative MSM reported having health insurance. A large proportion of men (64.1 %, 193 men) met the CDC recommended guidelines for PrEP. Age was associated with meeting PrEP guidelines; 80.0 % of young MSM age 18 to 24 years were eligible compared to 28.6 % of those 55 and older (p<0.001). No differences in the proportions meeting the guidelines for PrEP were noted by race/ethnicity, education level, income, and health insurance status.

Overall 30 men (9.9 %) reported using PrEP at some point in the past 12 months. Of note, two men (0.7 % of the sample of HIV-uninfected men) were reportedly using PrEP but did not fall under one of the guidelines for PrEP use. Amongst men using PrEP, the majority reported receiving PrEP from their doctor (93.3%). Amongst men who met recommended guidelines, PrEP use significantly differed by age (p=0.04) and race/ethnicity (p=0.02) (Table 2). No eligible individuals in the youngest age group (18–24 years) reported PrEP use, whereas 30 % of eligible men 55 years of age or older reported PrEP use. Compared to White MSM, fewer in other racial/ethnic groups reported PrEP use. In particular, eligible Hispanic men were less likely than eligible White men to report PrEP use (4.3 % vs. 22.9 %, respectively, age-adjusted risk ratio [RR] comparing Hispanics to Whites 0.2, 95 % confidence interval [CI] 0.0–0.8). Eligible Asian men and eligible Black men were also less likely to report PrEP use: 7.1 % of eligible Asian men and 7.7 % of eligible Black men reported PrEP use, compared to the 22.9 % of eligible White MSM. Eligible White men were over four times as likely as eligible non-White men to use PrEP (age-adjusted RR: 4.4, 95 % CI 1.6–11.9; results not shown in table).

In terms of willingness to use PrEP, 145 (48%) of the HIV-negative men reported that they would be willing to take PrEP. The proportion of each race/ethnicity group willing to take PrEP was similar (ranging from 43% to 54%).

While nearly two-thirds of MSM in San Francisco are eligible for PrEP, fewer than one in ten were using this prevention method two years after licensure and four years after it was found safe and efficacious [1, 14]. Using a published estimate of the size of the HIV uninfected MSM population in San Francisco [17] we estimate that 32,453 MSM would fall under the CDC guidelines of whom 4,708 were using PrEP in 2014. In other words, an additional 27,745 MSM in San Francisco would meet the guidelines but were not using PrEP.

While we found little difference in willingness to take PrEP across racial groups, we also found disparities in that PrEP use was disproportionately lower amongst young MSM and MSM of colour, particularly Black and or Hispanic men. Having health insurance was not correlated with PrEP use, suggesting that broad access to health care does not account for these disparities. Other studies have noted barriers to PrEP use amongst Black and Hispanic MSM, including perception of side effects [18] and cost [19]. A study of STI clinic attendees, including San Francisco, found MSM of colour less likely to have heard of PrEP and less likely self-refer for PrEP compared to White MSM [9]. Moreover, our data suggest that there is a discrepancy in the fact that similar proportions were willing to use PrEP by race/ethnic groups yet a paucity of Black and Latino MSM who were using PrEP at the time of the survey. A limitation of our behavioural surveillance-oriented survey is that we did not ask the specific reasons why persons did not use PrEP. We can nonetheless corroborate the potentially emerging PrEP disparity for these groups in the wider population.

Of course, our analysis has other limitations. First, as our data originate from a cross section survey we cannot ascribe causality to PrEP use. Indeed, our analysis does not include risk behaviours as temporality (e.g. cause before effect) cannot be established. However, the comparisons between those that are using and those that are not using PrEP is informative to describe PrEP use in a community-based sample and therefore also closer to a real-world settings. For example, our data can be used to advocate for programmes prioritising young and minority MSM. Second, our data are from 2014 when only a short time from licensure in 2012. The proportion of MSM using PrEP in San Francisco may well be larger at the time of this analysis. Third, although NHBS uses venue-based sampling as the national standard to sample MSM it is possible that our data miss some segments of the population or include those who may be more or less likely to use PrEP. Fourth, sample sizes are small given the low level of PrEP uptake so far, even in San Francisco where promotion has been vigorous. Collectively, these limitations highlight an important area for future research as PrEP use becomes more widespread. Lastly, our data are from San Francisco and do not reflect what may be occurring in other places in the US or internationally. For example, the demographic makeup of San Francisco MSM may differ from other populations of MSM in the U.S. and internationally. Unfortunately, sexual orientation is not yet included in the US Census and the sizes and make-up of MSM populations in the US are uncertain. However, with San Francisco being an early, vocal adopter of PrEP [4], our findings may provide a glimpse of one scenario that may play out elsewhere.

In conclusion, these findings call attention to the need to further monitor the rollout and uptake of PrEP in communities of MSM where it is recommended. PrEP uptake efforts should continue to attempt to reach Black and Latino MSM. If Black and Latino MSM do not take up PrEP use while White men do, it is possible that a greater share of new HIV diagnoses may occur amongst men of colour, exacerbating noted HIV disparities [12, 20, 21].