Associations between breast milk viral load, mastitis, exclusive breast-feeding, and postnatal transmission of HIV

Background. Exclusive breast-feeding is protective against postnatal transmission of human immunodeficiency virus (HIV), compared with mixed breast-feeding. Accordingly, exclusive breast-feeding for 6 months is the World Health Organization's recommendation to HIV-infected mothers for whom exclusive replacement feeding is not acceptable, feasible, affordable, safe, or sustainable. The mechanism of exclusive breast-feeding protection is unknown but is hypothesized to be mediated through reduced mastitis. Methods. We compared breast milk and plasma specimens of exclusive breast-feeding and mixed breast-feeding HIV- positive mothers archived from the ZVITAMBO trial in which mixed breast-feeding was associated with a 2-fold increased risk of postnatal transmission at 18 months. Plasma HIV load, breast milk HIV load and sodium/potassium ratio were measured as a proxy for subclinical mastitis. Results. Mixed breast-feeding was not associated with mastitis or breast milk HIV load. Mastitis was associated with breast milk HIV load, and this effect increased with increasing maternal plasma HIV load; mastitis was associated with postnatal transmission only when maternal plasma HIV load was high (>3.7 log₁₀ copies/mL). Initiation of breast-feeding within an hour of delivery was associated with exclusive breast-feeding (adjusted odds ratio, 1.62; 95% confidence interval, 1.02-2.58). Conclusions. Exclusive breast-feeding is associated with reduced postnatal transmission of HIV from mother to child, but this protection is not mediated by reduced mastitis or breast milk HIV load. The deleterious effect of mastitis increases as the mother's plasma HIV load increases.