HIV positive women are often told not to breastfeed in order to prevent transmission of the virus to their child. However, a new study suggests that this advice is overly cautious.

Researchers in South Africa compared transmission rates in exclusively breastfed infants, mixed fed and formula fed (never breastfed) infants to assess whether the pattern of feeding had any affect on early mother to infant transmission of HIV.

The study involved 549 HIV infected women who were part of a vitamin A intervention trial in Durban, and results were compared after three months.

At that time, 18.8 per cent of the never breastfed children were estimated to be HIV infected, compared with 14.6 per cent of breastfed children. What's more, the proportion of infants infected with HIV was significantly lower in the breastfed group than in the mixed feeding group, which had a 24.1 per cent infection rate.

The authors suggest that guidelines for HIV positive mothers should suggest exclusive breastfeeding and early weaning before or at three months to boost the child's immunity and prevent other infections from weakening the child's system.

They also suggest that in some cases a virus acquired during delivery could be neutralised by immune factors present in breastmilk (Lancet, 1999; 354: 471-6).