Self-harm among youth during the first 28 months of the COVID-19 pandemic in Ontario, Canada: a population-based study.

BACKGROUND: Youth have reported worsening mental health during the COVID-19 pandemic. We sought to evaluate rates of pediatric acute care visits for self-harm during the pandemic according to age, sex and mental health service use. METHODS: We conducted a population-based, repeated cross-sectional study using linked health administrative data sets to measure monthly rates of emergency department visits and hospital admissions for self-harm among youth aged 10-17 years between Jan. 1, 2017, and June 30, 2022, in Ontario, Canada. We modelled expected rates of acute care visits for self-harm after the pandemic onset based on prepandemic rates. We reported relative differences between observed and expected monthly rates overall and by age group (10-13 yr and 14-17 yr), sex and mental health service use (new and continuing). RESULTS: In this population of about 1.3 million children and adolescents, rates of acute care visits for self-harm during the pandemic were higher than expected for emergency department visits (0.27/1000 population v. 0.21/1000 population; adjusted rate ratio [RR] 1.29, 95% confidence interval [CI] 1.19-1.39) and hospital admissions (0.74/10 000 population v. 0.43/10 000 population, adjusted RR 1.72, 95% CI 1.46-2.03). This increase was primarily observed among females. Rates of emergency department visits and hospital admissions for self-harm were higher than expected for both those aged 10-13 years and those aged 14-17 years, as well as for both those new to the mental health system and those already engaged in care. INTERPRETATION: Rates of acute care visits for self-harm among children and adolescents were higher than expected during the first 2 and a half years of the COVID-19 pandemic, particularly among females. These findings support the need for accessible and intensive prevention efforts and mental health supports in this population.