Background: Trans women bear the highest burden of HIV of any population worldwide. For example, HIV prevalence is >30% in surveys of trans women in San Francisco. Unfortunately, the high burden is not matched by the availability of data to guide the HIV response. HIV-related data for trans women usually derive from studies that incorrectly aggregate them with men who have sex with men (MSM), include too few trans women to make inference to the population, or are severely biased by convenience sampling at clinics, service sites, or high-risk venues. Moreover, gender identity is not uniformly collected in national censuses and household surveys. To date, no study has directly measured the rate of HIV seroconversion among trans women in a population-based sample.
Methods: We established a longitudinal cohort study of trans women in the San Francisco Bay Area to measure HIV incidence from 2016-present. Participants were recruited through respondent-driven sampling (RDS) to gather a representative sample. HIV-negative trans women were followed every six months for 18 months with repeated HIV testing. Rates of seroconversion were calculated using the incidence density method assuming a Poisson distribution.
Results: A total of 429 HIV uninfected trans women were enrolled in the cohort; 412 had at least one follow-up visit and were included in analysis (96% retention). HIV incidence was 1.4 per 100 person-years (PY) (95% CI: 0.60-2.76). The majority of seroconversions (5/8) were among Latinas (incidence 2.76 per 100 PY). Preliminarily, incidence was very high among younger trans women ages 18-24 years (3.88 per 100 PY).
Conclusions: In San Francisco, a city heading toward zero HIV infections in other groups, our study witnessed a persistently high rate of seroconversion among trans women. This substantial transmission continues despite unparalleled access to gender-affirming medical procedures and social services. We will not reverse the course of the epidemic among trans women without addressing structural barriers and the low inclusion of trans women in research to design and test new biomedical HIV prevention interventions. Our cohort study provides much needed benchmark estimates to plan rigorous prevention trials with HIV incidence endpoints for trans women.