Breast-fed infants who are also given solid foods or milk from formula are at higher risk of HIV infection than those who are exclusively breast-fed, according to a study of mother-to-child transmission of HIV in KwaZulu Natal, South Africa.¹ Infants who receive such mixed feeding are more likely than those exclusively breast-fed to acquire HIV infection (hazard ratio, 10.9). Among infants who are exclusively breast-fed, those whose mothers have CD4 cell counts of fewer than 200 cells or 200–500 cells per microliter have elevated risks of getting infected (3.8 and 2.4, respectively) or not surviving HIV-free for six months after birth (4.0 and 2.3, respectively). Other factors associated with increased risk are a maternal age of 20–30, an infant birth weight of less than 2,500 g and labor lasting more than 12 hours.

The risk of mother-to-child transmission of HIV through breast-feeding in resource-poor countries has not been adequately examined, and there is some confusion regarding the recommendation of infant feeding options. Therefore, researchers conducted a nonrandomized intervention cohort study to assess the probabilities of HIV transmission and HIV-free survival associated with exclusive breast-feeding and other types of infant feeding during the first six months after birth.

Between 2001 and 2005, the study enrolled 1,372 HIV-infected women aged 16 or older who were attending antenatal clinics in Kwa-Zulu Natal. Antenatal CD4 cell counts were measured, and women were counseled about feeding options; those who chose to use formula were given a six-month supply. All women were provided with a single dose of nevirapine after enrollment or 28 weeks of gestation to be taken during delivery, and another dose to be given to the infant soon after birth. Following birth, counselors and clinic nurses supported mothers in their preference to breast-feed exclusively or to practice replacement feeding. (Exclusive breast-feeding was defined as receiving only breast milk, though water or formula was allowed on a total of no more than three days during the study period; replacement feeding was defined as receiving formula, with or without other liquids or solids.) Mothers reported feeding practices to independent monitors every week for six months; infants were tested monthly for HIV infection. Cumulative HIV transmission and infant mortality were determined using survival analyses, and regression analyses were used to assess associations between infection and mortality and various maternal and infant variables.

The median maternal age of HIV-infected mothers was 25. At the time of birth, 83% breast-fed exclusively, 8% practiced replacement feeding and 3% practiced mixed feeding (giving breast milk with formula, other liquids or solids); information was missing for the remaining women. Women who breast-fed exclusively were more likely than those who practiced replacement feeding to live in rural areas (45% vs. 30%) and were less likely to be urban dwellers (18% vs. 32%); equal proportions lived in semiurban areas (37–38%). Mothers' CD4 cell counts differed by feeding type: A higher proportion of women who practiced replacement feeding than of those who breast-fed their baby exclusively had counts of fewer than 200 cells per microliter (21% vs. 10%), and a lower proportion had counts of more than 500 cells per microliter (30% vs. 41%).

Of the 1,034 exclusively breast-fed infants for whom HIV test results were available, 175 were diagnosed as HIV-positive before six months of age; survival analysis found cumulative infection rates of 14% by six weeks and 20% by six months. Four percent of breast-fed infants who were uninfected at six weeks of age were infected by six months. Among exclusively breast-fed infants, estimated mortality at three months was 6%; among the infants given replacement feeding from birth, estimated mortality at three months was 15%.

Infants who received mixed feeding during their first six months were at higher risk of HIV infection than those who had breast-fed exclusively (hazard ratio, 10.9). Among the latter infants, transmission risk was associated with maternal CD4 cell counts: In a multi-variate analysis, those whose mothers had counts of fewer than 200 cells or 200–500 cells per microliter had a higher risk of HIV infection (3.8 and 2.4, respectively) than those whose mothers had counts of more than 500 cells per microliter. Other factors associated with an elevated risk of infection were having a mother aged 20–30 versus one younger than 20 (1.9), having a birth weight of less than 2,500 g versus a weight of more than 3,500 g (1.8) and being born after labor that lasted more than 12 hours versus less than four hours (2.2). In contrast, infants delivered by cesarean section rather than vaginally had a lower risk of infection (0.5).

Among infants who had breast-fed exclusively, the risk of not surviving HIV-free for six months after birth was similar to the risk of infection. Those whose mothers had counts of fewer than 200 cells or 200–500 cells per microliter had a higher risk of not surviving HIV-free (hazard ratios, 4.0 and 2.3, respectively) than those whose mothers had counts of more than 500 cells per microliter. An elevated risk was also found for infants whose mothers were aged 20–30 (1.5), who had a birth weight of less than 2,500 g (1.9) and who were born following labor that lasted more than 12 hours (2.3). Infants delivered by cesarean section were at lower risk of not surviving HIV-free for six months than those delivered vaginally (0.5).

According to the researchers, their findings on mother-to-child transmission of HIV confirm that exclusive breast-feeding is safer for infants of HIV-positive women than mixed feeding for the first six months after birth. Furthermore, the researchers believe that these findings "warrant revision of the present UNICEF, WHO, and UNAIDS infant feeding-guidelines," which recommend that HIV-infected women feed their infants commercial or home-prepared formula rather than breast milk when possible.—J. Thomas

REFERENCE

1. Coovadia HM et al., Mother-to-child transmission of HIV-1 infection during exclusive breastfeeding in the first 6 months of life: an intervention cohort study, Lancet, 2007, 369(9567):1107–1116.