Summary and Conclusion

Current scientific evidence provides the basis for the following statements and suggests areas where additional research is required.

Mother-to-child transmission of HIV

· The overall risk of mother-to-child transmission of HIV is about 15-25% among seropositive women who do not breastfeed (in the absence of interventions to reduce the likelihood of transmission), and between 25-45% among women who breastfeed.

HIV can be transmitted through breast milk

· The virus has been detected in components of breast milk.

· HIV infection has been found in infants of mothers who became infected with HIV during the breastfeeding period.

· Infants of HIV-negative mothers have been infected through exposure to HIV in unpasteurized breast milk from unscreened donors and HIV-infected wet-nurses.

· Infants diagnosed as HIV-negative at three months of age or later have been infected subsequently, with breastfeeding being the only risk factor.

Breastfeeding can be an important mode of mother-to-child transmission of HIV

· Where the mother has established HIV infection, the overall additional risk of HIV transmission during breastfeeding is at least 15%.

· In populations where breastfeeding is the main method of infant feeding, approximately one third of paediatric HIV is due to breast-milk transmission.

The mechanisms of breast-milk transmission are not yet fully understood

· The respective roles of cell-free and cell-associated HIV in breast-milk transmission are not known, nor is the association between plasma and milk virus levels understood.

· The portal of entry for the virus via infant mucosa requires further investigation.

Certain factors may increase the risk of HIV transmission through breast milk

· When a mother has been recently infected with HIV, the risk of transmission through breastfeeding may be twice as high as that of a women whose infection is already established (29% compared with 15%). This is probably due to high viral load occurring with recent infection. However, it is not clear whether a high serum viral load is correlated with a high viral load in breast milk. Further research is required.

· Increased risk of mother-to-child transmission is associated with markers of advanced HIV infection and maternal immunosuppression, including plasma viral load, clinical symptoms, and low CD4 and high CD8 cell counts. However, current knowledge about the role of maternal immunosuppression and advanced HIV disease in breast-milk transmission is limited and requires further investigation.

· Vitamin A deficiency is associated with an increased risk of overall mother-to-child transmission and with HIV in breast milk, but no studies have confirmed the role of vitamin A deficiency in increasing the risk of transmission through breastfeeding. Vitamin A supplementation has not been proved to be effective in reducing MTCT.

· Disruption of the epithelial integrity of the mucous membranes of the infant mouth or intestine (caused by nutritional or infectious factors such as mixed feeding and oral thrush), and nipple fissures may play a role in increasing the risk of transmission through breastfeeding. Research in this area continues.

· The effect on HIV transmission due to breastfeeding of giving AZT during pregnancy and delivery is not known, nor is the effect of postnatal treatment of breastfed infants with ARVs. Research is being carried out and results will be available in 1999.

Transmission can take place at any point during breastfeeding

· The risk of breast-milk transmission of HIV appears to be cumulative. The longer the duration of breastfeeding, the greater the additional risk of HIV transmission through breast milk.

· Because it is not known whether the risk of transmission differs at different times during lactation, the degree of efficacy resulting from early cessation of breastfeeding cannot be predicted.

· HIV has been detected in colostrum and mature breast milk; however, based on current evidence, it is not possible to establish the relative risks of transmission through colostrum and breast milk.

· Currently available diagnostic tools are inadequate for estimating risk associated with breastfeeding in the first few months of life. The risk of late postnatal transmission through breastfeeding is estimated to be 4-12%. This may possibly account for about half of transmission through breastfeeding.

The anti-infective properties of breast milk in the context of HIV

· HIV-positive women who breastfeed infants who are already infected with HIV may provide some protection against common childhood infections. Further research is required.

· Anti-infective substances in the breast milk of HIV-infected women, including immunoglobulins, lactoferin, and mucins, may target HIV, but further studies are needed to investigate the correlation between risk of transmission and the presence or absence of these substances.

The safety of different methods of infant feeding

· There is very little information on the safety and feasibility of infant-feeding alternatives for seropositive mothers and these aspects need to be studied (including commercial infant formula, homemade infant formula, heat-treated expressed breast milk, and wet-nursing). It is also important to identify approaches to treating expressed breast milk to eliminate the risk of transmission while preserving the milk's nutritional content.

· It is important to determine the efficacy of antiretroviral therapy given to the mother or the child during the breastfeeding period.

· Little is known about the effect of different feeding methods, including mixed feeding, on the course of HIV infection and other health outcomes in HIV-infected children.

Finally, research is needed on the effect of breastfeeding on the nutritional and immune status of the mother. The benefits of breastfeeding may be different for women infected with HIV.