Modeling the potential impact of viral load monitoring on vertical transmission of HIV in Kenya.

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Viral load (VL) monitoring among pregnant and breastfeeding women (PBFW) can reduce vertical transmission (VT) by identifying PBFW with unsuppressed VL and promoting re-suppression. However, the impact of varying degrees of adherence to VL monitoring guidelines on the prevention of vertical transmission (PVT) is unknown. We developed a microsimulation model of HIV progression and PVT care for PBFW living with recently acquired HIV in Kenya. We used this model to evaluate VL monitoring in two key maternal populations: 1) newly positive (NP) pregnant women who initiate ART during antenatal care and 2) known positive (KP) women who are diagnosed and initiate ART prior to conception. For each population, we simulated three levels of adherence to Kenyan VL monitoring guidelines during pregnancy and 18 months of breastfeeding: 1) No testing (NT); 2) 50% adherence to indicated VL tests (VL-50%); 3) 100% adherence (VL-100%). We evaluated VL monitoring in each population by comparing live births, maternal deaths, and VT under VL-50% and VL-100% to NT. Under NT, infants acquired HIV at a rate of 619 vs. 505 per 10,000 live births in the NP vs. KP populations, respectively. VL monitoring reduced VT by 1.6-2.7% in NP women vs. 9.1%-14.3% in KP women, and it reduced maternal deaths by 1.2-1.8% vs. 1.6-2.3%. Maternal VL monitoring in Kenya has considerably greater potential for achieving relative reductions in VT among KP women than among NP women. In KP women, even imperfect adherence to guidelines may achieve substantial relative reductions in VT.