Risk Factors for Vertical Transmission of Human Immunodeficiency Virus in Angola: A Case-Control Study

Vertical transmission of human immunodeficiency virus (HIV) remains a public health challenge in Angola despite the expansion of prevention of mother-to-child transmission (PMTCT) programmes. This study aimed to identify factors associated with vertical HIV transmission in a referral maternity hospital in Luanda. An observational case-control study was conducted using retrospective clinical and laboratory records from 2019 to 2024. A total of 204 mother-infant pairs were included, comprising 68 cases (HIV-infected infants) and 136 controls (HIV-exposed but uninfected infants), frequency-matched at a 1:2 ratio by infant year of birth and maternal age group. Infant HIV status was determined up to 18 months of age, or after breastfeeding cessation when applicable, according to the national diagnostic algorithm. Multivariable unconditional binary logistic regression was used, with matching variables retained in the model. Several factors were independently associated with lower odds of vertical transmission, including suppressed maternal viral load (adjusted odds ratio [aOR] = 0.07; 95% confidence interval [CI]: 0.03-0.20), adequate paediatric follow-up (aOR = 0.08; 95% CI: 0.02-0.27), caesarean delivery (aOR = 0.13; 95% CI: 0.04-0.37), maternal age over 25 years, formal education, adequate initiation of antiretroviral therapy during pregnancy, and attendance at four or more antenatal consultations. These findings suggest that gaps in the PMTCT cascade may be associated with residual vertical HIV transmission in this referral maternity setting. Given the observational design, these associations should not be interpreted as causal. Strengthening virological monitoring, treatment adherence support, and retention of mother-infant pairs in care remains an important programmatic consideration for PMTCT services.