Colostrum and mature milk

Cell-free and cell-associated HIV-1 have been detected in both colostrum and mature breast milk of women with established HIV infection. In a study in Haiti, HIV DNA (cell-associated virus) was detected in 70% of 47 colostrum samples and about 50% of breast-milk samples obtained at 6 (n=30) and 12 (n=15) months postpartum (Ruff et al., 1994). HIV DNA was detected in 47% of 129 samples of breast milk collected 15 days after delivery, and in 20% of 96 samples collected six months after delivery (Van de Perre et al., 1993). Both studies suggest a higher level of cell associated HIV in early milk compared to later, which would reflect the relatively high level of cells in colostrum compared to mature milk.

Somewhat differently, in a study in Kenya (Nduati et al., 1995) a higher proportion of samples of milk collected between seven days and six months had HIV DNA (65% of 108 breast milk samples) than did colostrum (51% of 77 samples) (p=0. 05). Among positive samples, the proportion of infected cells ranged from less than 1 in 10 000 cells to 1 in 3. High concentrations of HIV-infected cells were more common during the period 8-90 days after delivery than in samples taken either earlier or later. A second study quantified HIV-1 RNA (measuring cell-free virus) from breast-milk supernatants collected from the same group of women at the same times (Lewis et al., 1998). The range of viral concentration in the breast-milk supernatants was very wide and, although the difference was not statistically significant, viral load tended to be higher in milk collected more than 8 days after delivery than in milk samples taken earlier (p=0.10).

The potential effect of various factors makes it difficult to draw any conclusions about the relative risk of transmission through colostrum and mature breast milk. First, colostrum and mature breast milk contain different types of cells and different levels of immune modulating components (e.g. vitamin A, immunoglobulins and lactoferrin). Second, the total volume of colostrum ingested by the infant is much smaller than that of mature breast milk. Third, the infant's immune system is less well developed during the first few days of lactation than in later lactation, while younger infants have an increased blood concentration of maternal antibodies. In the study by Tess et al. (1998b), vertical transmission was not associated with a history of colostrum intake in 148 breastfed children.