Includes bibliographical referencesIntroduction: There is a large treatment gap for people with mental disorders in Africa and other low resourced countries, estimated to be between 70% and 90%. The treatment gap is mainly due to the lack of trained mental health professionals and inadequate mental health service resources in Africa. There has been a growing global movement championed by the World Health Organisation (WHO) to integrate mental health into primary health care as the most effective way of reducing this treatment gap. This study aimed to investigate the impact of WHO Mental Health Gap Action Programme (mhGAP) training and supervision on primary health workers' knowledge, attitudes, confidence and detection rate of major mental disorders in the district of Mulanje, Malawi. Method: The study was a quantitative evaluation using a quasi-experimental method (single cohort pre- and post-measures) and an interrupted time-series design. Forty-three primary healthcare workers from Mulanje, Malawi completed pre- and post- training questionnaires assessing knowledge, attitudes and confidence regarding the assessment and management of major mental disorders. Rates of diagnosis of major mental disorders were obtained from clinic registers for 5 months prior to and 7 months following training. Results: The results showed a significant change on knowledge and confidence scores but not attitudes. The mean knowledge score showed a statistically significantly increase from 11.8 (standard deviation [SD]: 0.33) before training to 15.1 (SD: 0.38) immediately after training; t(42) = 7.79, p <.01. Mean knowledge score was also significantly higher six month post training (13.9, SD: 2.52) than before training; t(42) = 4.57, p < .01. Similarly, the mean confidence score increased significantly from 39.9 (SD): 7.68) before training to 49.6 (SD: 06.14) immediately after training; t(84) = 8.43, p <.01. Mean confidence score was also significantly higher six month post training (46.8, SD: 6.03) than before training; t(84) = 6.60, p <.01. There was no overall significant difference in mean CAMI scores before, immediately after and 6 months after training in all four of the CAMI components. The F-test statistic and P-value for Authoritarianism, Benevolence, Social Restrictiveness and Community Mental Health Ideology were: F2, 126, 0.05 = 2.5; p =.09, F2, 126, 0.05 = 0.1; p =.9, F2, 126, 0.05 = 0.03; p = 1.0 and F2, 126, 0.05 = 0.04; p = 1.0, respectively. In the months January to May 2014 (before training), median number of cases per month was 77 (inter quartile range [IQR]: 65-87) whereas after training (months June to December) median number of cases was 186 (IQR: 175-197) showing a significant increase in median number of cases before and after the training; p =0.001. Conclusion: The results show clear improvements in the knowledge, confidence and detection of severe mental illness in primary care in Mulanje and demonstrate the potential for narrowing the treatment gap by rolling out mhGAP training nationally in Malawi. The findings of this study add to the growing evidence for policy makers of the effectiveness of mental health training and supervision of primary care workers in a resource-constrained country. Further research is needed to evaluate factors that may lead to change in health worker attitudes, to evaluate training and supervision programmes using more robust evaluation designs, such as randomised controlled trials, and to assess the scale up of mhGAP programmes at larger population levels
