Seroincidence and Clinical Manifestations of Entamoeba histolytica Among Belgian MSM in the PrEP Era: A Retrospective Cohort Study

BACKGROUND: Entamoeba histolytica (EH) has long been recognized as a sexually transmitted infection (STI); however, epidemiological data from nonendemic regions remain limited. OBJECTIVE: To assess the seroprevalence and seroincidence of EH among individuals attending a sexual health clinic in Belgium. METHODS: A retrospective cohort study was conducted at Universitair Ziekenhuis Brussel between October 1, 2022, and October 1, 2024. Residual sera from routine STI screenings were analyzed for EH-specific immunoglobulin G using an enzyme-linked immunosorbent assay. Inclusion required at least 2 samples collected 6 wk apart. Baseline seroprevalence and seroincidence were calculated. Additionally, a survey was distributed to members of the ESCMID Sexually Transmitted Infections Study Group to evaluate current diagnostic practices for EH in men who have sex with men across various countries. RESULTS: Of 577 individuals screened, 419 met the inclusion criteria. The baseline seroprevalence was 0.24% (n = 1). Seven participants seroconverted, yielding a seroincidence of 1.47 per 100 person-years (95% confidence interval: 0.59-3.03). No individual with positive serology originated from EH-endemic regions. Symptoms consistent with EH infection were reported in 3 cases, while 3 others exhibited possible signs during the seroconversion period. Only 1 individual underwent confirmatory fecal testing and received appropriate treatment. The survey response rate was 23%; 55% of respondents reported no EH diagnostic protocols in their sexual health clinics. Stool microscopy and molecular testing were preferred diagnostic tools, primarily for patients with procto-enteritis and negative STI workups. CONCLUSION: Greater awareness and effective diagnostic strategies for invasive EH infection are needed among men who have sex with men at elevated STI risk.