Background: To what extent antiretroviral therapy (ART) reduces mother-to-child HIV transmission (MTCT) during breastfeeding remains unclear. We assessed the MTCT risk from mothers on ART to their infants during breastfeeding.
Setting: Ifakara, rural Tanzania.
Methods: We included infants born between January 2013 and May 2016 to mothers who initiated ART before delivery, had a negative HIV DNA polymerase chain reaction at 4-12 weeks and exclusively breastfed for ≥6 months. Mothers' plasma HIV-RNA viral loads (VLs) were measured up to 11 months postdelivery. Infants were tested for HIV following national guidelines.
Results: Among 214 women with 218 pregnancies and 228 infants (10 twins), the median age at delivery was 33 years (interquartile range 28-36 years), and the mean time on ART was 23 months (interquartile range, 4-52 months). VL was measured twice in 53% (113/218) of pregnancies. During breastfeeding, 91% of mothers (199/218) had VL of <1000 copies per milliliter, and 75% (164/218) had <100 copies per milliliter. To November 2017, 8% (19/228) of infants were lost to follow-up (LTFU), 2% (5/228) transferred, and 8% (18/228) died before the determination of final HIV serostatus. Among the remaining 186 infants, 2 (1%; 95% confidence interval: 0.3% to 4%) were HIV positive: 1 born from a mother with high VL 1-month postdelivery and 1 from a mother who interrupted ART. Assuming a 15% MTCT risk through breastfeeding among the 42 infants LTFU, transferred, or dead, the overall MTCT risk would be 4%.
Conclusions: 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.