Breast milk transmission of HIV-1. Laboratory and clinical studies.

Breast milk transmission of HIV-1 can occur at any time during the entire duration of breastfeeding. The risk of late postnatal transmission (after 2.5 months of age) is 3.2 per 100 child/years of breastfeeding, but early postnatal transmission may be more frequent than previously thought. Exclusive breastfeeding has been suggested to be less risky than mixed feeding. Breast milk contains immunoactive cells, antiinfectious substances, immune globulins, cytokines, and complement factors. HIV-1 has been found in breast milk from HIV-infected mothers as both cell-associated and cell-free particles. Mastitis has been suggested to facilitate transmission of HIV-1. The portal of entry of HIV-1 in the infant mucosae may involve tonsilar lymphoepithelium, M cells, and enterocytes from intestinal surfaces. Anti-HIV-1 SIgA and IgM in breast milk and intestinal fluid may confer some protection. Transmission of HIV-1 by breastfeeding has to be taken into account in designing interventions to reduce/prevent mother-to-child transmission in developing countries.