The following is a summary of “Characteristics of the sexual networks of gay, bisexual, and other men who have sex with men in Montréal, Toronto, and Vancouver: implications for the transmission and control of mpox in Canada,” published in the February 2024 issue of Infectious Diseases by Xiu et al.
The 2022-2023 global mpox outbreak had a significant impact on gay, bisexual, and other men who have sex with men (GBM), with the majority of cases in Canada concentrated among this demographic, particularly in the urban centers of Montréal, Toronto, and Vancouver.
Researchers conducted a retrospective study to analyze the variations in the distributions of sexual partners by city and over time (2017-2023) and assess their association with mpox transmission.
They conducted the Engage Cohort Study (2017 to 2023), employing respondent-driven sampling to recruit 2,449 GBM in Montréal, Toronto, and Vancouver. Comparisons of reported sexual partner numbers over six-month periods were made across cities and three timeframes: pre-COVID-19 pandemic (2017-2019), pandemic (2020-2021), and post-restrictions (2021-2023). Bayesian negative binomial regressions and post-stratification, adjusted for sampling design and attrition, were utilized to model the distribution of sexual partners, and also estimated the basic reproduction number (ℛ0) of mpox through a risk-stratified compartmental model.
The results showed that before the COVID-19 pandemic, the distributions of sexual partner numbers were comparable across cities: the mean number of partners over the last 6 months was 10.4 (95% CrI: 9.4-11.5) in Montréal, 13.1 (11.3-15.1) in Toronto, and 10.7 (9.5-12.1) in Vancouver. Partner numbers decreased in all cities during the pandemic. Following the lifting of restrictions, sexual activity increased but remained below pre-pandemic levels. Based on reported cases and post-restrictions distributions of sexual partners, the estimated ℛ0 for mpox varied from 2.4-2.7 between cities. The estimated mpox per-partnership transmission probability was 84% (uncertainty ranging from 51-98%). Cumulative incidences (0.7-0.9%) were similar across cities.
Investigators concluded that GBM sexual activity hasn’t fully rebounded after restrictions were lifted, though similar partner distributions suggest comparable mpox ℛ0 risks across cities, necessitating continued vaccination and surveillance efforts.