The study, published in the April 29th edition of the journal AIDS, also showed that amongst children who were exclusively breastfed, only 1.31% became infected with HIV during the first six months of life, suggesting that early weaning as practiced in a number of ongoing studies could reduce the risk of HIV transmission through breastfeeding.
A previous study carried out in South Africa (Coutsoudis 2001) showed that after 18 months of follow-up, infants that were breastfed exclusively were significantly less likely to become infected with HIV. However, children exposed to any breastfeeding in this study were significantly more likely to be HIV-positive after 18 months than those who received formula feed.
Mixed feeding, in which infants are exposed to breast milk and to other liquids, as well as solid food and formula feed or cows milk, is associated with a higher rate of HIV transmission, probably due to exposure to allergens that irritate the gut and lead to inflammation, thus increasing the risk of HIV infection from breast milk.
Mixed feeding is very common in African countries, and although solid food may be introduced as early as three months in many African countries, breastfeeding will frequently continue alongside solid foods for 18 months after birth.
Since exclusive formula feeding is not practical in many African settings due to the cost, lack of clean water and the risk of social stigma if mothers do not breastfeed, safer alternatives to mixed feeding need to be identified.
The Zvitambo study was designed to assess the impact of vitamin A supplementation on maternal and infant health, and also collected data to confirm whether exclusive breastfeeding was safer than mixed feeding. It enrolled 14,110 mother/infant pairs at the time of delivery. 4495 mothers (31.9%) were HIV-positive at the time of enrolment.
Complete data were available for 2060 infants of HIV-positive mothers, with a further 918 excluded because they tested HIV-RNA positive by week 6, 64 due to death before week 6, and 515 due to the lack of an HIV RNA test at week 6. The vast majority of additional exclusions were due to a single missed clinic visit.
HIV testing of mothers was carried out at enrolment, six weeks, three months and three monthly thereafter, and blood samples were also taken from infants at these intervals. Mothers did not automatically receive the results of their HIV antibody tests, but were encouraged to request for them.
Mothers were questioned in detail at each visit about infant feeding practices, and feeding was only classified as exclusive breastfeeding if there was no more than one lapse from exclusive breastfeeding in any three month period, and if this lapse was confined to a liquid substitute for breast milk. Any use of solid foods during the study was classified as mixed feeding.
Predominant breastfeeding was classified as breastfeeding plus liquid feeding, with any use of solid feeding during the study classified as mixed feeding.
One hundred and ninety-nine infants became infected with HIV after week 6, and postnatal transmission at months 6, 12 and 18 was 3.9%, 7.7% and 12.1% respectively. Sixty-eight per cent of infections due to breastfeeding occurred after month 6, with the highest rate of transmission in the mixed feeding group.
Cumulative percantage of infants infected by feeding group, and relative risk of infection compared to exclusive breastfeeding
|*p=0.05 p=0.0009 *p=0.02 (differences between
exclusive and predominant non-significant)
Maternal CD4 cell count below 350 at baseline was predictive of transmission through breastfeeding at 12 months and 18 months, but not at month 6. Maternal CD4 cell count below 200 was predictive of transmission through breastfeeding at all time points, and women in this category had a ninefold higher risk of transmitting HIV through breastfeeding by month 6. Severe maternal anaemia at baseline (maternal haemoglobin below 70g/l) was also highly predictive of transmission at all time points.
The investigators comment: Our findings underscore the importance of supporting exclusive breastfeeding, particularly in areas of high HIV prevalence where many women do not know their HIV status, and among HIV-positive mothers who choose to breastfeed...Among breastfeeding women known to be HIV-positive, early breastfeeding cessation should be considered, along with support for nutritionally adequate, safe replacement feeding. HIV-positive mothers with CD4 cell counts less than 200 cells/mm3 should be strongly encouraged to consider antiretroviral treatment while breastfeeding, or replacement feeding from birth because of their very high risk of postnatal transmission.
Coutsoudis A. Method of feeding and transmission of HIV-1 from mothers to children by 15 months of age: prospective cohort study from Durban, South Africa. AIDS 15:379-387, 2001.
Iliff PJ et al. Early exclusive breastfeeding reduces the risk of postnatal HIV-1 transmission and increases HIV-free survival. AIDS 19: 699-708, 2005. (Source:AIDSMAP, 26 April, 2005 http://www.aidsmap.com/en/news/2CE28909-E352-4CB0-89CE-1E1272D10B92.asp).