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O04.2 The impact of COVID-19 and associated response measures on STI transmission among MSM: a mathematical modelling study

Background Fear of COVID-19 infection and the response measures have affected sexual behaviours of men who have sex with men (MSM) and access to care for sexually transmitted infections (STI). We investigated whether these changes resulted in increased or decreased STI transmission among MSM. Methods We developed a mathematical transmission model for chlamydia and gonorrhoea among MSM. We accounted for 15–35% reduction in the number of casual partners and 50–80% reduction in STI testing during lockdowns (March-May 2020; October 2020 to February 2021); these reductions were 0–10% and 20–35%, respectively, in periods with less restrictive COVID-19 measures (June-September 2020, March-August 2021). Reductions until August 2020 were estimated from Dutch data; other reductions were based on expert opinion. We assumed no changes after August 2021. Two scenarios were examined: with home-testing (in 25% of cases not tested at healthcare facilities) and without home-testing. We calculated the percentage change in prevalence due to COVID-19 associated changes, compared to prevalence in the same year without changes due to COVID-19. Results From the model, we estimated an increase of 8.4% (interquartile range (IQR), 7.6–9.4%) in chlamydia prevalence and an increase of 7.5% (IQR, 6.0–8.9%) in gonorrhoea prevalence at the end of 2020 without home-testing, compared to the prevalence without COVID-19 associated changes. The increase subsided in 2021, but chlamydia and gonorrhoea prevalence remained higher than without COVID-19 until 2025. With home-testing, the percentage increase in 2020, compared to the scenario without COVID-19, was 5.3% (IQR, 4.6–5.9%) for chlamydia and 3.5% (IQR, 2.6–4.4%) for gonorrhoea prevalence. Conclusion The COVID-19 pandemic may have resulted in an increase in chlamydia and gonorrhoea prevalence in 2020. The increase can be smaller after 2020, if STI testing at healthcare facilities and/or at home increases. The findings emphasize the importance of facilitating STI (self) care in times of crisis.