Applying Implementation Science to Scale Up Collaborative Care for Depression in Primary Healthcare Across South South Nigeria

Collaborative care is an evidence-based model for integrating mental health into primary care, yet its scale-up in sub-Saharan Africa requires rigorous implementation science investigation. This study applies implementation science to examine the scaling up of a collaborative care model for depression across primary healthcare facilities in South South Nigeria, covering Akwa Ibom, Cross River, Rivers, Bayelsa, Delta, and Edo States. A hybrid effectiveness-implementation type II design will be used, simultaneously evaluating patient outcomes and implementation processes across 30 primary health centers. The collaborative care intervention will include systematic depression screening (PHQ-9), care manager coordination, stepped medication management, and psychiatric supervision through telemedicine. Implementation outcomes including fidelity, reach, adoption, sustainability, and equity will be assessed using the Proctor taxonomy. Patient outcomes including depression remission (PHQ-9 below 5), functional recovery (Sheehan Disability Scale), and quality of life (WHOQOL-BREF) will be measured at 6 and 12 months. Multilevel regression will examine patient and facility-level predictors of implementation success. This study produces original implementation science evidence from six states, directly informing the National Primary Health Care Development Agency's mental health integration strategy. Keywords: collaborative care, depression, implementation science, primary healthcare, South South Nigeria