Among infants born to HIV-positive mothers, those who are breastfed for more than 15 months or who develop oral thrush within six months after birth have an elevated risk of postnatal infection. Their risk is also increased if their mother has nipple or breast lesions during breastfeeding or if her immune system is compromised, according to a study of 412 exclusively breastfed children born to HIV-positive mothers in Nairobi, Kenya.¹

The large majority of childhood cases of HIV-1 infection are acquired from the child's mother, whether before, during or after birth. Though measures such as antiretroviral medications and avoidance of breastfeeding reduce mother-child transmission, these interventions are often unavailable or impractical in the low-income countries where the burden of HIV is highest. For example, parents in these countries generally cannot afford antiretroviral medications or breast-milk substitutes, nor can governments afford to provide them to all the women who need them. Identifying the risk factors in mothers and children that place a child at particularly high risk for contracting HIV after birth and that are amenable to intervention may allow limited resources to be used to the greatest effect.

To identify these risk factors, researchers followed 412 children born to seropositive mothers at a large maternity hospital in Nairobi for several years, with 871 infants born to seronegative women forming a control group. The HIV status of the mother and child were determined at the time of delivery; at frequent follow-up clinic visits, clinicians rechecked HIV status, performed CD4 cell counts and examined both mother and baby. None of the women or children received antiretroviral medications.

Children were generally classified as having acquired HIV postnatally if they seroconverted after testing negative for HIV for at least three months after birth. Only children who were followed for at least 12 months were included in the study analysis. Of the 412 children born to HIV-positive mothers, 37 became infected in the postnatal period, 51 became infected at or before birth and 310 remained HIV-negative.

In a bivariate analysis, maternal nipple lesions (usually cracked nipples) during breastfeeding and breastfeeding for more than 15 months more than doubled the risk of infant infection (odds ratios of 2.3 and 2.4, respectively), while breast in- flammation (mastitis) and infant oral thrush before six months of age almost tripled the risk (2.7 and 2.8, respectively). Moreover, the odds of HIV infection among infants whose mother had a CD4 cell count of less than 400 mm³ were more than four times those of other infants. Of 12 children born to women who seroconverted while breastfeeding, five became infected, suggesting that timing of maternal seroconversion is an important risk factor. Nevertheless, the number affected was too small for meaningful analysis.

In a multivariate logistic regression analysis, the effects of low maternal CD4 cell count, infant oral thrush before six months of age, breastfeeding for more than 15 months and maternal mastitis or breast lesions remained significant. The analysis indicated, however, that children who were breastfed for more than 15 months did not have the same increased risk of infection from maternal nipple or breast lesions as did those who were weaned before that point. The researchers surmise that perhaps only lesions serious enough to cause a mother to shorten the duration of breastfeeding affect the risk of HIV transmission.

The authors point out that several of the risk factors identified in their analysis are amenable to intervention. They note, for example, that treating infants against thrush at birth could lower the risk of HIV infection by preventing thrush-related inflammation of the oral and gastrointestinal tract. The investigators also suggest that mothers should be counseled on ways of preventing nipple cracking and on the importance of seeking prompt treatment for the condition. Where early weaning is feasible, they say, it should be encouraged. They stress, however, that since no screening or intervention program can totally prevent transmission of HIV from mother to child, the most effective means is the prevention of maternal infection.--A. Brochert

REFERENCE

1. Embree JE et al., Risk factors for postnatal mother-child transmission of HIV-1, AIDS, 2000, 14(16):2535-2541.