We found no MTCT from mothers who were retained in care and had suppressed VL. Breastfeeding signifies a very low risk when mothers adhere to ART. Adherence counseling, VL monitoring, and strategies to trace back those LTFU should be a priority.

Background Poor adherence to antiretroviral drugs and viral resistance are the main drivers of treatment failure in HIV-infected patients. In sub-Saharan Africa, avoidance of treatment failure on second-line protease inhibitor therapy is critical as treatment options are limited. Methods In the prospective observational study of the Kilombero & Ulanga Antiretroviral Cohort in rural Tanzania, we assessed virologic failure (viral load �1,000 copies/mL) and drug resistance mutations in bio-banked plasma samples 6-12 months after initiation of a protease inhibitor-based treatment regimen. Additionally, viral load was measured before start of protease inhibitor, a second time between 1-5 years after start, and at suspected treatment failure in patients with available bio-banked samples. We performed resistance testing if viral load was �1000 copies/ml. Risk factors for virologic failure were analyzed using logistic regression. Results In total, 252 patients were included; of those 56% were female and 21% children. Virologic failure occurred 6-12 months after the start of a protease inhibitor in 26/199 (13.1%) of adults and 7/53 of children (13.2%). The prevalence of virologic failure did not change over time. Nucleoside reverse transcriptase inhibitors drug resistance mutation testing performed at 6-12 months showed a positive signal in only 9/16 adults. No cases of resistance mutations for protease inhibitors were seen at this time. In samples taken between 1-5 years protease inhibitor resistance was demonstrated in 2/7 adults. In adult samples before protease