O13.5 - Characteristics of mpox positive, versus mpox negative, and mpox unsuspected clients from the Centre of Sexual Health, Public Health Service of Amsterdam, 20 May to 15 September 2022

Background


In May 2022 multiple European countries reported the first cases of mpox (monkeypox) infection, predominantly among men having sex with men (MSM). In the subsequent weeks, over 100 countries reported increasing numbers of mpox infections among MSM. We aimed to identify behavioral and clinical characteristics of mpox cases to further strengthen case definitions.





Methods


We analysed data from all Amsterdam Sexual Health Center MSM clients. We compared mpox positive clients with mpox negative clients, and clients unsuspected for mpox (those not meeting the UK mpox case definition). We describe continuous variables using the median and interquartile range (IQR) and categorical variables using absolute numbers and percentages. Continuous variables were compared between groups using the non-parametric Kruskal-Wallis test; categorical variables were compared between groups using the Pearson’s χ² or Fisher’s exact tests. Ct values (as a proxy for viral load) of different anatomical sites of mpox positive clients were compared with Kruskal-Wallis test.





Results


From 20 May 2022 to 15 September 2022, we tested 374 MSM for mpox. In the same period, 6,932 MSM mpox unsuspected clients were not tested. Of the 374 MSM tested, 135 (36%) were positive for mpox. Comparing the mpox positive, mpox negative and unsuspected groups, the mpox positive MSM were older (median age respectively 36, 34, and 34 years, p=0.019) and more often lived with HIV (30% versus 16% and 7%, p< 0.001). Furthermore, mpox positive patients more often reported receptive anal sex without a condom, sexualised drug use, more sex partners, and were more often diagnosed with bacterial STI (p < 0.001). Systemic symptoms and anogenital lesions were associated with mpox infection. For mpox positive patients, anal samples (p=0.009) and lesional samples (p=0.006) showed significantly lower median mpox Ct values compared to throat samples (figure).





Conclusion


The results described here have been used to prioritise prophylactic vaccination to


MSM most exposed to mpox. The anal site and suspected lesions had a significantly higher mpox viral load than the throat. Therefore, our study supports the notion that in the current mpox outbreak among MSM, sexual contact is the main transmission route, and not airborne transmission.