Breastfeeding approximately doubles the risk of vertical transmission. [2] Studies have not been able to show that duration of breastfeeding has an effect, [3] but infants uninfected at 3-6 months of age are still at risk of becoming infected through breastfeeding. [4] Previous findings from Durban, South Africa, showed that the highest overall rate of vertical transmission was in exclusively breastfed children (39%), and lowest in never-breastfed infants (24%), with no evidence of a duration effect in the exclusively breastfed group. [5]
In this issue of The Lancet, Anna Coutsoudis and colleagues present a further potentially important piece of the puzzle that addresses the issue of transmission and breastfeeding in the first 3 months of life. In their cohort of 549 infants born to HIV-1-infected women, samples from infants were tested by HIV-DNA PCR on day 1 and at ages 1 month and 3 months. Exclusively breastfed infants were substantially less likely to be infected at 3 months than were those receiving mixed feeding or those never breastfed. The carefully collected information on infant feeding and the strict definition of exclusive breastfeeding enabled an assessment of risk of vertical transmission in the first 3 months by feeding method. Similar percentages of exposed infants had evidence of infection at birth-about 6%-but differences in vertical transmission had emerged by 1 month and had become larger by the time the babies were 3 months old.
However, before a rush into implementation, the results of this study need to be carefully assessed. Infants were tested only at birth and at 1 month and 3 months of age. If the increase in the percentage infected reflects acquisition of infection around the time of delivery, that in the never-breastfed group (6.4% to 14.8% to 18.8%), like the increasing trend in the mixed-feeders group, is surprisingly protracted. [6] And why was there only a small increase in the proportion infected in the breastfeeding group at 1 month (from 6.8% at birth to 8.7%) but a much steeper increase at 3 months (to 14.6%)? The absolute increases in percentage infected were similar for the three groups between 1 month and 3 months, and the real difference seems to have occurred in the first month of life. Would this finding suggest a protective early effect of exclusive breastfeeding? [7] More frequent sampling for PCR in these first 3 months of life would enable examination of the pattern of time to positive PCR in the three groups.
These findings suggest that, if HIV-1 infected women choose to breastfeed, they should refrain from giving any other foods, at least for the first 3 months. In view of the risk of late postnatal transmission through breastmilk after 3-6 months, [4] and because introduction of other foods becomes more frequent as the infant gets older, women could then be advised to consider early and abrupt weaning. But it is premature to base public-health guidelines on the basis of the results of this one study, and further research is urgently required to confirm and elucidate the findings.
What next? Longer follow-up is required to clarify whether these infants continue to acquire the infection after 3 months of age, and whether the risk will remain associated with type of feeding. The role of breast health, mastitis, cracked nipples, infant attachment, and other variables needs to be investigated, and the baby's susceptibility to infection needs to be assessed. Further research is also needed on the acceptability of exclusive breastfeeding and early weaning, on whether the regimen of exclusive feeding for 3 months followed by early and complete weaning is practicable, and on whether this regimen will interfere with the promotion of breastfeeding in the general population. The results presented in this paper highlight the need for re-evaluation of the role of breastfeeding in transmission of HIV-1.
Department of Epidemiology, Institute of Child Health, University College London, London WC1N 1EH, UK
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