Quantifying the risk of breast-milk transmission

Early studies investigating the frequency of breast-milk transmission and associated factors were limited by small numbers as well as by the predominance of one method of infant feeding in any one cohort (European Collaborative Study, 1992; Ryder, 1991; Blanche et al., 1989; Tovo et al., 1988).

In 1992, a meta-analysis was carried out using data from four studies reporting on 42 recently infected women and six studies reporting on 1772 women with established infection. The majority of the women had breastfed for 2-4 weeks, and 106 women had breastfed for longer than six months. The estimated additional risk of transmission from breast milk, above that occurring during pregnancy and delivery, among women with established HIV infection, was approximately 15% (95% Confidence Interval 7-22%) (Dunn et al., 1992). However, 15% may be an under-estimation among women who breastfeed for longer periods of time.

The risk of transmission through breast milk among women with recent infection (HIV infection acquired in the postpartum period) was nearly twice as high (29% (95% CI 16-42%)).

Insufficient information is available to estimate the exact association between duration of breastfeeding and the risk of transmission. However, there is strong evidence for a gradual and continued increase in transmission risk as long as the child is breastfed (Taha et al., 1998, Leroy et al., 1998).