The impact of the COVID-19 pandemic on hospital admissions for psychiatric disorders: results from the multicentre CoMeH study on the Italian population Running title: The impact of COVID-19 on hospital admissions for psychiatric disorders

Background. To evaluate the impact of the COVID-19 pandemic on hospital admissions for psychiatric disorders, with a focus on the patients’ socioeconomic and demographic characteristics and/or the diagnostic group and type of admission. Methods. Open cohort of individuals aged ≥ 10 years resident for at least two years in one of three large areas of Italy. The outcome was the first admission for a psychiatric disorder (First Mental Health Admission: FMHA) during the study period (January 2018–December 2021). Municipality of residence, sex, census tract deprivation index, citizenship, type of admission and the diagnostic group were considered as covariates of interest. Incidence rate ratios of FMHAs were estimated via an interrupted time series (ITS) analysis using a step-change negative binomial model. Moreover, an ITS analysis was conducted on the monthly number of FMHAs to evaluate the impact of COVID-19 on the temporal trend of FMHAs. Results. Of the 5,159,363 subjects enrolled, 11,171 had an FMHA in the study period. The incidence of FMHAs decreased after the outbreak of the pandemic, overall and by sex, deprivation level and citizenship. Immigrants from high migration pressure countries (HMPCs) had a greater reduction in FMHAs during COVID-19. A decrease in FMHAs was observed for all diagnoses, the only exceptions being for post-traumatic stress and related disorders, which increased. Involuntary admissions also increased dramatically at the outbreak of the pandemic. Younger age (< 34) and high deprivation level were associated with higher risk of hospitalization. In the following post-outbreak period (March 2020-December 2021), a moderate but significant growing trend of FMHAs was observed, although not reaching the pre-pandemic levels. A more robust increase was found especially for patients with eating disorders, while FMHAs for patients with post-traumatic stress and related disorders decreased to the low pre-pandemic levels. Involuntary FMHAs also decreased in the post-outbreak period. Conclusions. The pandemic had a considerable, and in some cases dramatic, impact on hospitalizations for psychiatric disorders. However, the effect appeared temporary, suggesting that the expectations of a dramatic surge in mental health issues due to the pandemic could have been overemphasized, at least in the short term. Longer follow-up surveys are needed.