Seroprevalence and predictors of Hepatitis A virus immunity among young MSM in urban Brazil: a cross-sectional study at a referral center

In addition to the usual socioeconomic and sanitary exposures to the Hepatitis A Virus (HAV), men who have sex with men (MSM) are also exposed through sexual behavior. Objective: This research aims to estimate the HAV seroprevalence and its predictors among young MSM. Methods: This cross-sectional study, conducted in Rio de Janeiro, Brazil, included participants sequentially between 2019 and 2022. Inclusion criteria were cisgender males aged 18 to 35 who reported sex with men in the previous six months, had never received the HAV vaccine, and had no chronic immune-mediated conditions. Predictors represented sexual practices, use of different substances, sexually transmitted infections, signs or symptoms, water consumption and sanitation, and socio-demographics. The outcome of all the analyses was HAV serology (positive vs. negative). The main analysis compared the prediction performances of the random forest regression model with penalized GLM with internal cross-validation or bootstrap. Results: The HAV seroprevalence was 39.6%. The compared models included from 16 to 42 predictors, always representing all predictor dimensions. "Chemsex" was identified as a predictor of HAV seroprevalence. A generation effect and interactions among race, education, and source of income were also identified as HAV predictors. The best model had excellent calibration and moderate discrimination with an area under the ROC curve of 0.714 and an R2 of 0.187. We provide a web calculator at https://pedrobrasil.shinyapps.io/INDWELL/. Conclusion: This study reveals a high susceptibility of cisgender young MSM to HAV infection. These findings highlight the enduring impact of socioeconomic inequities on enteric virus exposure and underscore the need for targeted public health strategies. One may use the prediction model to estimate the risk of seropositivity/susceptibility to HAV in aid of deciding either to perform an HAV test or to vaccinate against HAV, or even to estimate HAV seroprevalence in MSM populations where the HAV test is not easily available.