First implementation of a collaborative care model for common mental disorders in primary care in France: fidelity of care manager intervention matters

Background: Care for common mental disorders relies on primary care, where they often remain undiagnosed and untreated. The collaborative care model (CoCM) is a team-based approach involving care managers (CMs) who work alongside general practitioners and remote psychiatrists to provide evidence-based mental healthcare. Between 2021 and 2023, a pilot study implemented the CoCM for the first time in France in four primary care practices with nurses with previous professional experience in psychiatry acting as the CMs. As part of the implementation research of this pilot, we analyzed the fidelity of the CM intervention to the original CoCM. We examined CM process of care metrics and explored their association with initial symptom severity and patient outcomes - an aspect rarely addressed in previous international implementation research on the CoCM. Methods: Using electronic medical records, we calculated several fidelity measures for CM intervention, including early intervention (time to first intervention), intensity of care (number of visits and intervention duration) and evidence-based care (type of care provided). We also examined potential variations according to initial symptom severity, in line with a stepped-care approach. Patient outcomes, particularly depression response and remission, were analyzed according to initial symptom severity and fidelity measures. Results: A total of 235 patients were included in the study. Overall, the care provided by CMs aligned with the original CoCM, in terms of early intervention, intensive care, and type of evidence-based care delivered. It was also adjusted according to patients' initial symptom severity, in particular for early intervention, in line with a stepped-care approach. Higher fidelity of the CM intervention to the CoCM - especially shorter time to treatment initiation and number of visits - was associated with better patient outcomes. Conclusions: The CoCM shows promise for improving the treatment of common mental disorders in French primary care within a stepped-care framework. Its extension will require ensuring high fidelity of the CM intervention to the model in real-world settings, as it appears crucial for achieving optimal patient outcomes. These findings also provide useful lessons for other countries implementing the CoCM.