Associate Medical Officer of Health Toronto Public Health Toronto, Ontario, Canada
Project: In the summer of 2022, Toronto, Canada experienced an outbreak of mpox ( >500 confirmed cases), disproportionately affecting the gay, bisexual and men who have sex with men (gbMSM) community. Case counts declined following the implementation of a large pre-exposure immunization campaign. In early 2023, cases of mpox resurged in Toronto.
Issue: Several studies are ongoing to understand the transmission dynamics of mpox. The relative importance of asymptomatic transmission is unknown. As case counts declined in Toronto in the fall, so did testing for the virus. It was unclear whether undetected and / or asymptomatic cases in the fall of 2022 led to the resurgence of cases detected in 2023. A review of Monkeypox virus wastewater surveillance and whole genome sequencing (WGS) was conducted to generate hypotheses about the source of the 2023 resurgence. A communications plan was created and information was shared with community partners, health professionals and the public to encourage uptake of 2nd doses of Imvamune.
Results: The review of local wastewater surveillance data for mpox correlated well with reported case detections, decreasing in the fall, and increasing with the winter resurgence. WGS sequence provided lineage information, placing sequences in a phylogenetic context. The mpox cluster in early 2023 was most similar to sequences from another country, suggesting a new importation as a source for the recent cases. Second dose vaccine coverage was estimated to be only 9% in January. In March 2023, text reminders were sent to approximately 17,000 individuals who were eligible to receive a second dose of vaccine.
Lessons Learned: It is important to be prepared for resurgences of mpox in communities. Surveillance through case detection and testing can be complemented by wastewater and WGS analysis. In our experience, ongoing local undetected transmission was not a likely contributor to the resurgence however; further research into this area is of high priority to establish better ongoing prevention and control. Our experience highlights some of the lessons for managing a resurgence of mpox, including the importance of ongoing efforts to promote vaccine uptake.
