Mother-to-child transmission of HIV-1 infection during exclusive breastfeeding in the first 6 months of life: an intervention cohort study

Background: Exclusive breastfeeding, though better than other forms of infant feeding and associated with improved child survival, is uncommon. We assessed the HIV-1 transmission risks and survival associated with exclusive breastfeeding and other types of infant feeding. 

Methods: 2722 HIV-infected and uninfected pregnant women attending antenatal clinics in KwaZulu Natal, South Africa (seven rural, one semiurban, and one urban), were enrolled into a non-randomised intervention cohort study. Infant feeding data were obtained every week from mothers, and blood samples from infants were taken monthly at clinics to establish HIV infection status. Kaplan-Meier analyses conditional on exclusive breastfeeding were used to estimate transmission risks at 6 weeks and 22 weeks of age, and Cox's proportional hazard was used to quantify associations with maternal and infant factors. 

Findings: 1132 of 1372 (83%) infants born to HIV-infected mothers initiated exclusive breastfeeding from birth. Of 1276 infants with complete feeding data, median duration of cumulative exclusive breastfeeding was 159 days (first quartile [Q1] to third quartile [Q3], 122-174 days). 14·1% (95% CI 12·0-16·4) of exclusively breastfed infants were infected with HIV-1 by age 6 weeks and 19·5% (17·0-22·4) by 6 months; risk was significantly associated with maternal CD4-cell counts below 200 cells per μL (adjusted hazard ratio [HR] 3·79; 2·35-6·12) and birthweight less than 2500 g (1·81, 1·07-3·06). Kaplan-Meier estimated risk of acquisition of infection at 6 months of age was 4·04% (2·29-5·76). Breastfed infants who also received solids were significantly more likely to acquire infection than were exclusively breastfed children (HR 10·87, 1·51-78·00, p=0·018), as were infants who at 12 weeks received both breastmilk and formula milk (1·82, 0·98-3·36, p=0·057). Cumulative 3-month mortality in exclusively breastfed infants was 6·1% (4·74-7·92) versus 15·1% (7·63-28·73) in infants given replacement feeds (HR 2·06, 1·00-4·27, p=0·051). 

Interpretation: The association between mixed breastfeeding and increased HIV transmission risk, together with evidence that exclusive breastfeeding can be successfully supported in HIV-infected women, warrant revision of the present UNICEF, WHO, and UNAIDS infant feeding guidelines.