A two year study of mothers and babies in Kenya has found that formula feeding of babies born to HIV-positive mothers reduces the risk of infant seroconversion by almost half (44%).
A reduction of transmission of this degree, note the investigators, is equivalent to that seen in short-course zidovudine (AZT) studies carried out in Cote D'Ivoire and Burkina Faso.
Six months of formula feeding in Nairobi costs about £190 ($300).
The study
425 HIV-positive mothers were enrolled at a Nairobi antenatal clinic and randomised to formula feeding or breastfeeding of their babies. Unsurprisingly, compliance to the assigned method of feeding was higher in the breastfeeding group (96% vs 70%), and compliance with formula feeding was strongest in women with more advanced HIV disease and higher viral load. 68 mother-infant pairs were lost to follow-up during the study.
After two years of follow-up, 36.7% of the infants in the breastfeeding arm were HIV-positive, compared to 20.5% in the formula feeding arm. 44% of the infections in the breast feeding arm were thus attributable to breast feeding, and 75% of infections are estimated to have occurred in the first six months. However, the researchers warned that their study does not answer the question of when most breast feeding transmissions occur.
Overall mortality was similar in both arms. 24.4% of infants in the breastfeeding arm had died after two years, compared with 20% of infants in the formula feeding arm. These rates are higher than the norm for Nairobi, but not unusual in a cohort of HIV-infected women. Amongst infants proven to be HIV-free the death rate was higher in the breastfeeding arm than the formula feeding arm.
In an accompanying review of how to prevent mother to child transmission in resource-poor countries, Dr Kevin de Cock recommends that cup feeding rather than bottle feeding is preferable in resource-poor countries, due to the difficulty of sterilising feeding bottles. He also emphasises the importance of access to clean water supplies. In the Nairobi cohort all women had access to clean water.
If women with HIV choose to breast feed, "early weaning as soon as the infant can take adequate replacement food seem appropriate". Weaning is recommended at around six months in cases where formula feeding is not possible, and prolonged breast feeding after six months of age continues to carry a risk.
Women who breastfeed should be encouraged to use condoms with their partners during the breastfeeding period, despite the contraceptive effect of breastfeeding. This is because women exposed to HIV during this period are at especially high risk of transmitting HIV in breast milk.
References
De Cock K et al. Prevention of mother to child HIV transmission in resource poor countries: translating research into policy and practice. Journal of the American Medical Association 283 (9): 1175-1182, 2000.
Nduati R et al. Effect of breastfeeding and formula feeding on transmission of HIV-1: a randomized clinical trial. Journal of the American Medical Association 283 (9): 1167-1174, 2000.