Serological Markers of Selected Sexually Transmitted Infections (HBV, HCV, HIV, and Syphilis) in Patients with Anogenital Warts: A Two-Centre, Five-Year Study

Background: Human papillomavirus-induced disruption of the anogenital mucosal barrier may increase susceptibility to other sexually transmitted infections (STIs), and guidelines recommend STI screening in patients with anogenital warts (AGW). We aimed to determine the seroprevalence of concomitant STIs in patients with AGW over a five-year period and to perform an exploratory assessment of associated demographic factors. Methods: In this retrospective, cross-sectional study, all consecutive patients clinically diagnosed with AGW between December 2020 and October 2025 (n = 779) were evaluated. Serological results for HBsAg, anti-HBs, anti-HCV, anti-HIV, and syphilis (treponemal and non-treponemal) were obtained. Seroprevalence was estimated with Wilson 95% confidence intervals (CIs) using the number of patients actually tested as the denominator. Patterns of multiple reactive serological markers were described, and the relationship between age and seropositivity was examined using a Cochran–Armitage trend test. Associations of demographic factors with concomitant STI seropositivity were explored using Fisher’s exact test with Woolf logit CIs and a complementary Firth penalized logistic regression; given the small number of events, these analyses were considered exploratory and hypothesis-generating. Results: Among 779 patients (585 [75%] male; mean age, 35.80 ± 12.32 years), the overall seroprevalence of concomitant STIs was 2.4% (19/779; 95% CI, 1.6–3.8). Seroprevalence was 1.4% for HBsAg, 0.9% for anti-HCV, 0.2% for anti-HIV, and 1.6% for treponemal antibodies, while anti-HBs immunity was present in 53.5% of patients. Two patients (10.5% of seropositive cases) had more than one concomitant STI. Seropositivity increased from 0.7% in patients aged 17–24 years to 3.5% in those aged ≥45 years, although the trend was not statistically significant (p = 0.13). Anti-HBs negativity was associated with concomitant STI seropositivity (OR = 5.63; 95% CI, 1.60–19.83; p = 0.003); this association was attenuated and no longer statistically significant after excluding HBV markers (OR = 2.73; 95% CI, 0.70–10.69; p = 0.200). A complete-case analysis restricted to patients with a fully defined testing panel yielded a similar prevalence estimate (2.8%; 95% CI, 1.7–4.5). Conclusions: The seroprevalence of the tested markers in patients with AGW was low but non-negligible and increased with age, while the subgroup of markers more consistent with current infection was less common. Anti-HBs negativity was associated with the composite outcome, but a sensitivity analysis showed this was largely attributable to its expected link with HBV status. These findings support guideline-recommended serological screening—including hepatitis B vaccination assessment—in all patients with AGW, and should be regarded as hypothesis-generating given the limited number of seropositive cases.