Trends in HIV Incidence among Female Sex Workers and Men who Have Sex with Men in Nairobi, Kenya, 2009-2021.

Female Sex Workers (FSW) and men who have sex with men (MSM) in Kenya remained disproportionately burdened by HIV. Our study aims to estimate trends in HIV incidence and identify characteristics associated with the rate of infection among these populations over the past decade. Data were collected at Sex Workers Outreach Program (SWOP) in Nairobi County from 2009 to 2021. We included records of 3,595 FSW and 581 MSM with a negative HIV test at enrolment and at least one follow-up test. We compared survival time between MSM and FSW using the Kaplan Meier log-rank test and used multiple Poisson regression to estimate incidence rate ratios. A steady decline in HIV infection was observed from 2009 to 2019 but increased in 2020 and 2021. The crude incidence rate was 1.46 (95% CI: 1.29-1.65) cases per 100 person-years. The incidence rate among MSM was 8.08 (6.73-9.69) per 100 person-years and 0.8 (95% CI: 0.7-1.0) per 100 person-years of follow-up among the FSW. In multivariate analysis, MSM had 16.14 times the risk of HIV infection compared to FSW (95% CI: 9.20-28.32), with relative risk declining in older age groups until over 50, where MSM and FSW experienced similar risk. For every successive year since 2009, the risk of HIV infection declined (annual IRR:0.73, 95% CI: 0.71-0.75). Continued and accelerated efforts targeted at MSM and FSW are needed to ensure the observed decline in HIV incidence continues in line with the UNAIDS-2030 global targets.