Odyssée: protocol for a prospective cohort on psychiatric transition at age 17 in Nice, France

The transition from child and adolescent mental health services (CAMHS) to adult mental health services (AMHS) represents a critical period of vulnerability, often marked by care discontinuities and adverse clinical outcomes. International studies have highlighted the risks associated with this transition, but local epidemiological data remain scarce in France. The Odyssée study aims to provide local data to inform the development of structured transition pathways.

This prospective monocentric cohort study will be conducted at Lenval University Children's Hospital in Nice, the only paediatric hospital providing dedicated child psychiatry emergency services in the Alpes-Maritimes department. Recruitment started in April 2026 and is ongoing at the time of manuscript submission. Study completion is anticipated in September 2028. The primary objective is to determine the annual prevalence of 17-year-olds living in Nice who attend child and adolescent psychiatry services using administrative data combining census counts from the French National Institute of Statistics and Economy Studies and hospital discharge records (Programme de médicalisation des systèmes d'information (PMSI)).In parallel, a prospective cohort of 100 adolescents aged 17 years will be followed for 12 months to address secondary objectives, including clinical profiles, care trajectories, transition readiness, clinical outcomes and determinants of care continuity. Assessments will be conducted at baseline, 6 months and 12 months using validated instruments (Mini International Neuropsychiatric Interview-simplified (MINI-S), WHO Quality of Life-brief (WHOQOL-BREF), Health of the Nation Outcome Scales for Children and Adolescents (HoNOSCA), Transition Readiness and Appropriateness Measure (TRAM), Transition Related Outcome Measure (TROM)). Descriptive and multivariable analyses will be performed to identify factors associated with continuity of care. This study is expected to provide one of the first city-level estimates of psychiatric transition needs in France and contribute to the international literature on continuity of care, youth mental health trajectories and transitional service organisation.

The study has been approved by the Comité de Protection des Personnes Sud-Ouest et Outre-Mer IV (approval number 2025-A01581-48). Written informed consent will be obtained from participants and one parent or legal guardian. Findings will be disseminated through peer-reviewed publications, scientific conferences and reports to regional health authorities.

NCT07068945.