Incidence and Sociocultural Determinants of Postnatal HIV Transmission Among HIV- Exposed Infants in Manyara Region, Tanzania: A Mixed-Methods Study

Background Despite substantial achievements in scaling up the Prevention of Mother-to-Child Transmission (PMTCT) of HIV in Tanzania, new pediatric HIV infections persist, particularly during the postnatal period. Understanding the incidence of infection and the sociocultural factors influencing transmission is crucial to achieving the elimination of mother-to-child transmission (eMTCT) goals by 2030. Methods: A mixed-methods convergent parallel design was used. Quantitative data were extracted from a retrospective cohort of 797 HIV-exposed infants and their mothers enrolled in PMTCT services in the Manyara Region between 2019 and 2023. Incidence rates were computed per 1000 person-months. The qualitative component involved 26 mothers of HIV-exposed infants and 5 healthcare providers interviewed using a grounded theory approach to explore sociocultural, behavioural, and systemic factors influencing postnatal HIV transmission. Thematic analysis was conducted using NVivo 12. Results: Among 797 HIV-exposed infants, 17 (2.1%) tested HIV-positive by 18 months, giving an incidence rate of 1.92 per 1,000 person-months (95% CI: 1.19-3.09). Most infections occurred between 3 and 15 months postpartum. Four qualitative themes explained persistent transmission: (1) stigma and non-disclosure undermining adherence, (2) traditional and economic influences on feeding, (3) health system challenges, and (4) peer and community support as enablers. Conclusion: Despite high PMTCT coverage, postnatal HIV infections persist in Manyara Region. The incidence remains low but concentrated during the breastfeeding period. Sociocultural and systemic barriers continue to compromise ART adherence and safe infant feeding. Strengthening community-based adherence support and addressing stigma and traditional practices are critical to sustain eMTCT progress.