O5.4 - Age patterns of HSV-2 incidence and prevalence in two communities in Rakai, Uganda: a catalytic incidence model applied to population-based seroprevalence data
Background: Herpes simplex virus type 2 (HSV-2) is an incurable sexually transmitted infection (STI) that causes painful genital ulcers and is associated with increased risk of acquiring and transmitting HIV. Population-level serostudies on HSV-2 incidence and prevalence, which could help target HSV-2 and HIV prevention measures towards the most at-risk groups, are generally lacking. We therefore aimed to quantify HSV-2 prevalence and risk factors for infection, and infer age-patterns of incidence in south-central Uganda.
Methods: We measured HSV-2 prevalence from cross-sectional serological data from men and women aged 18-49 in the STI Prevalence Study (STIPS), under the Rakai Community Cohort Study (RCCS) in Rakai, Uganda. Population-based data were collected from all consenting adults in the two study communities: an inland agrarian community and a Lake Victoria fishing community, known to have dramatically different HIV incidence and prevalence. We used Poisson regression to examine factors associated with HSV-2 seropositivity, compared HIV prevalence by HSV-2 serostatus by gender and 5-year age band, and calibrated a catalytic model using Bayesian methods to infer HSV-2 prevalence and incidence by age.
Results: Overall, among 1,825 participants, measured HSV-2 prevalence was 53.6% (95% confidence interval (CI):51.3%-55.9%). Prevalence increased with age and was higher among women in the fishing community, in whom it reached 95.0% (95% credible interval (CrI):90.8%-97.4%) by age 49. Modelled annual incidence increased steeply in late adolescence, rising to 10.2% (95%CrI:6.6%-14.2%) by age 20 among women in fishing communities and 5.7% (95%CrI:3.9%-7.9%) inland. Estimated mean age of HSV-2 infection was 18-21 in women and 21-23 in men. Individuals living with HIV were significantly more likely to be HSV-2 seropositive; HIV prevalence was ten-fold higher in people with HSV-2: for example, 54.1% (95%CI:44.8%-63.2%) of 30-35-year-old women with HSV-2 were living with HIV versus 4.8% (95% CI 0.6%-16.2%) of their HSV-2-negative peers.
Conclusion: HSV-2 prevalence and estimated incidence in this population were extremely high, with most infections occurring at young ages. Interventions seeking to reduce HSV-2 burden, such as future HSV-2 vaccines or therapeutics, must reach young target populations. The remarkably higher HIV prevalence among individuals with HSV-2 underscores this population as a priority for HIV prevention.
