Determinants of vertical transmission of HIV infection in Kilifi County, Kenya: a case-control study

Introduction: mother-to-child transmission of Human Immunodeficiency Virus (HIV) remains a significant contributor to pediatric HIV infections in Kenya despite expanded prevention services. Persistent gaps along the prevention of mother-to-child transmission (PMTCT) cascade continue to undermine elimination efforts. Methods: we conducted a retrospective, unmatched case-control study using routinely collected PMTCT data from selected health facilities in Kilifi County, Kenya. The cases were HIV-positive mothers whose HIV-exposed infants tested HIV-positive by deoxyribonucleic acid polymerase chain reaction (DNA PCR), while controls were HIV-positive mothers whose infants tested HIV-negative during the same period. Maternal and infant PMTCT cascade indicators were assessed. Associations between PMTCT service uptake and infant HIV status were examined using chi-square tests and multivariable logistic regression. Results: a total of 161 mother-infant pairs were included (59 cases and 101 controls). Failure to attend antenatal care, lack of maternal antiretroviral therapy (ART) during pregnancy, non-disclosure of HIV status, and home delivery were significantly associated with infant HIV infection. Maternal ART uptake during pregnancy was the strongest protective factor against vertical transmission (adjusted odds ratio 30.23; 95% CI: 7.56-120.96). Conclusion: missed opportunities along the PMTCT cascade, particularly poor antenatal care (ANC) attendance and delayed or absent maternal ART, remain key drivers of residual mother-to-child HIV transmission in Kilifi County. Strengthening retention, timely ART initiation, and continuity of care across the PMTCT cascade is critical to achieving elimination of vertical HIV transmission.