Timing of HIV transmission during breastfeeding

Transmission of HIV through breast milk can take place at any point during lactation. The persistence of maternal antibodies and the presence of a "window period" during which infection is undetectable using currently available technology, make it impossible to determine whether an infant has been infected during delivery (intrapartum) or through breastfeeding in the period following birth. Therefore, when seropositive women breastfeed their infants, it is not possible to differentiate between HIV transmission attributable to delivery and that resulting from breastfeeding from birth. (Newell, 1998; Bobat et al., 1997; Mandelbrot et al., 1996; Bertolli et al., 1996; Simonon et al., 1994; Datta et al., 1994).

Later postnatal transmission through breastfeeding can be determined using currently available diagnostic tools. Studies of infants found to be negative by PCR testing at 2-6 months of age, but who subsequently showed evidence of infection, have provided estimates of the risk of late postnatal transmission (after 3-6 months of age) ranging from 4-12% (Ekpini et al., 1997; Karlsson et al., 1997; Bertolli et al., 1996; Simonon et al., 1994).

Table 2. Studies of the risk of late postnatal transmissions