(P209) The impact of the mpox epidemic on the trends of sexually transmitted infections among male HIV positive individuals and HIV PrEP users in Belgium. Results from an STI clinic.

Background: The European mpox epidemic started suddenly in May 2022 and unexpectedly decreased sharply after July-August 2022. One of the explanations could be that there was a behavioral change among men who have sex with men (MSM) due to more awareness of mpox transmission. A behavioral change such as a reduction in unsafe sexual intercourse would translate into a decrease in Chlamydia trachomatis/Neisseria gonorrhoeae (CT/NG) cases. Our aim was to assess the impact of the mpox epidemic on the trends of CT/NG among male HIV-positive and HIV-PrEP users in an STI clinic in Antwerp, Belgium.

Methods: The monthly number (May to November) of CT/NG requests in 2022, including the positivity ratio for CT and NG was compared with 2021 using chi-2 (positivity ratio) or poisson regression (number of requests).

Results: The overall positivity ratio for CT/NG during the entire study period -May to November 2022- (305/1913; 15.9%) was comparable to the same period in 2021 (338/1955; 17,3%, p=0.261). Interesting differences between 2022 and 2021 were, however, noted in the CT/NG positivity ratio for the months May and August (Table 1). While the number of requests remained comparable between May 2021 and May 2022 -marking the beginning of the epidemic-, proportionally more CT/NG cases were detected in May 2022 (22.8%) compared to May 2021 (13.6%). In contrast, proportionally fewer CT/NG cases were detected in August 2022 (12.4%) compared to August 2021 (20.5%). Yet again, the number of CT/NG requests did not differ between August 2021 and August 2022. Of note, the amount of CT/NG test requests was lower in October 2022 compared to October 2021.

Conclusion: The decline in the positivity ratio of CT/NG in August 2022 is suggestive of a change in sexual behavior among male HIV-positive and HIV-PrEP users. This behavior change could have contributed to the sharp decline in mpox observed in the following period. However, monthly fluctuations of the CT/NG positivity ratio in this population are common, so these results should be interpreted with caution and should be confirmed by a study reviewing the sexual behavior data of this population in both periods.