Strengthening malaria case management in Plateau State through on-the-job mentorship and supervision: evaluating the effects of targeted capacity building on diagnostic accuracy and data quality

Malaria remains a leading cause of morbidity and mortality in Nigeria, where weaknesses in diagnosis, treatment, and data quality persist. This study evaluated the impact of an integrated on-the-job mentorship and supportive supervision (OJMS) model on malaria case management in Plateau State. We conducted a retrospective analysis of data from 125 purposively selected health facilities (2012–2024), categorized into comprehensive support (technical + commodities) and technical-only groups. Data were extracted from outpatient registers, District Health Information System 2 (DHIS2), and supervision checklists. Analyses included descriptive statistics, correlation, t-tests, Analysis of Variance (ANOVA), and multivariable linear regressionResults: Diagnostic coverage increased from 41% (95% CI 38–44) to 97% (95% CI 95–98). Confirmed malaria cases rose 5.6-fold, a change most consistent with improved case detection rather than a true rise in transmission. Provider compliance with Artemisinin-based Combination Therapy (ACT) increased from 40% (95% CI 37–43) to 96% (95% CI 94–98; p < 0.001). Health worker knowledge scores improved from 50 to 86%, and supervision frequency increased by 238%. Reporting timeliness improved from 54 to 94%, and illogical data entries declined from 20 to 3%. Spatial analysis revealed higher case detection in the Northern Zone (associated with mining and rainfall) and higher ACT compliance in the Central Zone (with internally displaced populations). In this retrospective, non-randomised evaluation, implementation of the OJMS model was associated with marked improvements in core malaria case-management competencies and health-system processes. The concurrent rise in confirmed cases most likely reflects enhanced detection rather than rising transmission, although the observational design precludes firm causal attribution. These findings suggest that continuous, embedded mentorship is a promising and potentially scalable approach to strengthening malaria case management in Nigeria and similar high-burden settings, and warrants confirmation in controlled studies.