A retrospective analysis of COVID-19 clusters in the Québec population from 2020 to 2022.

Throughout the pandemic, COVID-19 cases tended to organize into spatial clusters. In the absence of individual and/or network information on cases, however, surveillance systems face challenges in identifying the pathways through which these clusters emerge. Using Québec COVID-19 surveillance data from 2020 to 2022, this study identified characteristics associated with the likelihood of being among the first cases in a cluster. Our results show that young adults were consistently at higher risk of constituting the first cases of large community clusters across all waves, suggesting that closer monitoring of COVID-19 incidence in this age group could be pivotal for early detection of emerging clusters or new waves. Overall, our study provides valuable insights for public health authorities by helping to identify priority groups at the forefront of cluster emergence and by supporting the development of tailored and adaptive interventions.