P18 - Impact of the COVID-19 pandemic on the hospitalization rates for mental health conditions and self-harm in children and adolescents in metropolitan France

The long-term impact of the COVID-19 pandemic on the mental health of children and adolescents is yet unknown. The aim of this study was to assess the impact of the COVID-19 pandemic on the rates of hospitalizations for mental health (MH) conditions and self-harm (SH) among children and adolescents (aged 6 to 17) in metropolitan France three years after the pandemic onset. This is a national cohort study based on hospital medico-administrative data (PMSI) collected in the pre-pandemic onset period (Jan. 2016 - Feb. 2020), initial pandemic period (March 2020 - May 2020), 1st post-pandemic year (June 2020 - May 2021), 2nd post-pandemic year (June 2021 - May 2022), and 3rd post-pandemic year (June 2022 - May 2023). Monthly hospitalization rates per 100,000 children and adolescents were modeled using a time-series analysis to assess changes in monthly rates and temporal trends and to calculate cumulative percent differences between estimated and expected hospitalization rates in each post-pandemic period. The analysis was stratified by age and sex groups (children/adolescents; boys/girls), and by specific MH diagnosis. A total of 583,244 hospitalizations (18.6% children and 81.4% adolescents) were analyzed: 81.4% were related to a MH condition and 18.6% were related to intentional SH. Before the pandemic onset. increasing trends were observed only for SH hospitalizations During the initial pandemic period, all rates immediately decreased. Trends of hospital admissions for MH conditions increased during the first post-pandemic year and decreased thereafter. Trends for SH admissions increased in the first two post-pandemic years, and decreased in the third. Overall, in the 1st post-pandemic year, the rate of hospital admissions for MH decreased by 3% [-6.9%; 0.8%], and increased for SH by 8% [-1.5%; 17.9%] compared to the expected rates. During the 2nd post-pandemic year, cumulative percent increases were observed for both MH and SH hospitalization rates (+5.5% [4.7%; 6.4%] and +39.1% [38.7%; 39.5%], respectively). In the 3rd post-pandemic year, the rate of hospitalizations for MH decreased by 3.1% [-4.9%; -1.2%] and that for SH exceeded the expected rate, by 28.9% [25.7%; 32.2%]. The rate of hospital admissions increased for behavioral syndromes associated with physiological disturbances (mainly eating and sleep disorders) compared to the expected rates in all post-pandemic years, and for mood disorders in the second post-pandemic year only. While significant variations were observed between the different age and sex groups, adolescent girls were the most impacted patient group. The impact of the COVID-19 pandemic on hospitalizations for specific mental-health conditions and self-harm in children and adolescents remains significant three years after the onset of the COVID-19 pandemic, especially in adolescent girls.