Differential impact of the COVID-19 pandemic on chlamydia and gonorrhoea cases among youth and young adults in Canada: an interrupted time series analysis.

Introduction: Globally, access to sexual health services declined during the COVID-19 pandemic. In Canada, pre-existing provincial differences in the organisation and delivery of sexual health services may have influenced how the pandemic affected testing and case detection. This study assessed the immediate and sustained impacts of the pandemic on reported chlamydia and gonorrhoea cases among youth and young adults in Ontario and British Columbia. Method: Laboratory-confirmed cases of chlamydia and gonorrhoea among individuals aged under 25 years were analysed using data from provincial surveillance sources from 2016 to 2021. Interrupted time series analyses were conducted using seasonal autoregressive integrated moving average models, stratified by sex and province. Sensitivity analyses examined trends excluding the initial 5 months of the pandemic (March-August 2020) and examined sustained impact through 2023. Results: Following the onset of COVID-19, chlamydia rates declined immediately by 39.13 cases per 100 000 population (95% CI -45.76 to -32.50) in Ontario and by 23.13 per 100 000 (95% CI -27.91 to -18.35) in British Columbia, corresponding to cumulative relative reductions of 42% and 29%, respectively. Gonorrhoea rates decreased by 3.25 per 100 000 (95% CI -4.72 to -1.77) in Ontario and by 1.70 per 100 000 (95% CI -3.92 to 0.51) in British Columbia, translating to cumulative relative reductions of 37% and 22%. Declines in reported cases were more pronounced among females for chlamydia, while males exhibited more sustained decreases over time. Sensitivity analyses confirmed these significant declines after excluding the initial pandemic period and persistent reductions through 2023. Conclusion: Reported chlamydia and gonorrhoea rates among youth and young adults declined substantially during the pandemic, with greater decreases in Ontario than in British Columbia. Sustained reductions suggest ongoing underdiagnosis and underreporting. British Columbia's smaller declines may be partly explained by broader access to their online testing services, GetCheckedOnline.