Introduction: In the mpox / monkeypox outbreak of 2022, Berlin registered the highest number of cases in Germany, almost all in men-who-have-sex-with-men (MSM). However, the frequency of clinically inapparent infections is largely unknown
Methods: We retrospectively tested anal, urethral and pharyngeal swabs from three community-based anonymous STI-testing centers in Berlin mostly visited by MSM for mpox virus DNA using the NovaplexTM MPXV Assay. These centers offer HIV/STI testing primarily for asymptomatic individuals, while people with symptoms are mostly referred to medical care. Individuals are requested to self-complete an anonymous questionnaire on sociodemographic data and sexual behavior. For this analysis, we used descriptive methods, Wilcoxon rank-sum tests for comparison of medians and χ2-test to compare categorical variables.
Results: Between 13 April and 28 October 2022, we retrieved 5413 samples from 3640 individuals, of which 3634 (99.8%) had a valid test result. 76 individuals (2.1%) tested positive for mpox virus in at least one of the swabs. The proportion of clinically inapparent mpox infections in the anonymous samples peaked in June 2022 with 5.9% (37/630) of the tested samples, similar to the peak of mpox cases reported through the statutory notification system (Figure 1).
We obtained anonymous questionnaire data for 3393 individuals (93.4%). The majority were cisgender men (88.5%), followed by non-binary persons (6.6%), cisgender women (2.2%), transgender women (1.0%), and transgender men (0.6%) – other/missing: 1.0%. 80.1% identified as MSM. No mpox infections were detected among cisgender heterosexual men and cisgender women (n=293).
Persons testing positive for mpox reported more partners in the previous 6 months (median 11 partners vs 5 partners in persons testing negative, p< 0.001) and were more likely to currently use HIV pre-exposure prophylaxis (PrEP) (4.8% vs. 1.0%, p< 0.001).
Conclusion: Testing of anonymous samples of persons from STI testing centers did not yield indication of mpox circulation in Berlin prior to May 2022 before any cases were notified, or in October 2022 when the number of notified cases was low. Persons with higher partner numbers and PrEP users were more likely to have clinically inapparent mpox infections at the time of sampling.
