Tracing defaulters in HIV prevention of mother-to-child transmission programmes through community health workers: results from a rural setting in Zimbabwe

Introduction: High retention in care is paramount to reduce vertical human immunodeficiency virus (HIV) infections in prevention of mother-to-child transmission (PMTCT) programmes but remains low in many sub-Saharan African countries. We aimed to assess the effects of community health worker-based defaulter tracing (CHW-DT) on retention in care and mother-to-child HIV transmission, an innovative approach that has not been evaluated to date. Methods: We analyzed patient records of 1878 HIV-positive pregnant women and their newborns in a rural PMTCT programme in the Tsholotsho district of Zimbabwe between 2010 and 2013 in a retrospective cohort study. Using binomial regression, we compared vertical HIV transmission rates at six weeks post-partum, and retention rates during the perinatal PMTCT period (at delivery, nevirapine [NVP] initiation at three days post-partum, cotrimoxazole (CTX) initiation at six weeks post-partum, and HIV testing at six weeks post-partum) before and after the introduction of CHW-DT in the project. Results: Median maternal age was 27 years (inter-quartile range [IQR] 23 to 32) and median CD4 count was 394 cells/mu L-3 (IQR 257 to 563). The covariate-adjusted rate ratio (aRR) for perinatal HIV transmission was 0.72 (95% confidence intervals [95% CI] 0.27 to 1.96, p = 0.504), comparing patient outcomes after and before the intervention. Among fully retained patients, 11 (1.9%) newborns tested HIV positive. ARRs for retention in care were 1.01 (95% CI 0.96 to 1.06, p = 0.730) at delivery; 1.35 (95% CI 1.28 to 1.42, p<0.001) at NVP initiation; 1.78 (95% CI 1.58 to 2.01, p<0.001) at CTX initiation; and 2.54 (95% CI 2.20 to 2.93, p<0.001) at infant HIV testing. Cumulative retention after and before the intervention was 496 (85.7%) and 1083 (87.3%) until delivery; 480 (82.9%) and 1005 (81.0%) until NVP initiation; 303 (52.3%) and 517 (41.7%) until CTX initiation; 272 (47.0%) and 427 (34.4%) until infant HIV testing; and 172 (29.7%) and 405 (32.6%) until HIV test result collection. Conclusions: The CHW-DT intervention did not reduce perinatal HIV transmission significantly. Retention improved moderately during the post-natal period, but cumulative retention decreased rapidly even after the intervention. We showed that transmission in resource-limited settings can be as low as in resource-rich countries if patients are fully retained in care. This requires structural changes to the regular PMTCT services, in which community health workers can, at best, play a complementary role.