Incidence rates of diagnosed anxiety and depressive disorders in Québec, Canada: changes in trends after the COVID-19 pandemic using interrupted time series methods.

Abstract

The COVID-19 pandemic had profound effects on mental health worldwide. Within Canada, the province of Québec experienced high increases in mental health distress and implemented particularly strict public health measures. These unique characteristics motivate the examination of the local experience of the COVID-19 pandemic. This study aimed to examine changes in incidence rates of diagnosed anxiety and depressive disorders in Québec, Canada before and after the COVID-19 pandemic. Analyses drew on administrative health records from the Québec Integrated Chronic Disease Surveillance System from January 2010 to March 2022 (147 months). The setting for analyses was the province of Québec, Canada. The analytical sample covered January 2010 to March 2022 (147 months) for all individuals aged 15 years and older (men and women) eligible for the Québec public health insurance plan. Interrupted time series methods were used to estimate counterfactual trends of monthly incidence rates of diagnosed anxiety and depressive disorders under conditions with and without the impact of the COVID-19 pandemic. Analyses adjusted for local public health policies, including the enactment of the <i>Cannabis Act</i> (2018) and major provincial health system reforms (2015). As we drew on count data, we used generalised linear modelling techniques with Poisson distribution to estimate predicted and counterfactual incidence rates of diagnosed anxiety and depressive disorders over time. We report regression results as the incidence rate ratio (IRR) with 95% CIs. Following the onset of the COVID-19 pandemic, monthly incidence rates of diagnosed anxiety disorders were 4.9% <i>higher</i> (IRR: 1.049, 95% CI 0.955 to 1.153), but there was insufficient evidence of a statistically significant change; there was a statistically significant increase in the slope by 1% (IRR: 1.010, 95% CI 1.00 to 1.018). For diagnosed depressive disorders, monthly incidence rates were rather 3.6% <i>lower</i> (IRR: 0.965; 95% CI 0.904 to 1.030), although not statistically significant; there was a statistically significant increase in the slope by 1.4% (IRR: 1.014; 95% CI 1.008 to 1.020). Results from the counterfactual trends suggest that incidence rates of diagnosed anxiety disorders would have been lower (observed rates are higher), while incidence rates of depressive disorders would have been higher (observed rates are lower) had the COVID-19 pandemic not occurred. Findings encourage further consideration of the indirect consequences of public health crises and related responses on population mental health. They also highlight the need to examine dynamics in local jurisdictions and support reflection on policy investments in mental health protection and promotion.