s
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South Africa Breast-fed (n = 394) 6.9 19.9 21.8 24.2 31.6
Formula (n = 157) 7.6 18.0 18.7 19.4 19.4
Kenya Breast-fed (n = 191) 7.0 19.9 24.5 28.0 36.7
Formula (n = 193) 3.1 9.7 13.2 15.9 20.5
Brazil Breast-fed (n = 168) 21.0
Formula (n = 264) 13.0
Note: A dash indicates data is not available. Infants were categorized either as breast-fed (predominantly mixed
breast-fed) or fed formula (never breast-fed). Source: Coovadia and Coutsoudis (2001).
Knowledge of Infant s HIV Status
When infants are diagnosed as hiv-positive, it is di~cult to determine
whether the virus was transmitted during the pregnancy, the birth process, or
breast-feeding. It is commonly assumed that increases in viral load over time in
breast-fed infants are attributable to the breast-feeding. However, the viral load
in the infant can increase after birth even in the absence of breast-feeding. Con-
sider table 12.1, on the rates of virus transmission for breast-fed and formula-fed
infants in several di’erent studies.
In the South Africa and Kenya studies, not only the breast-fed infants but also
the formula fed infants appear to have had increasingly high rates of infection
over time. Comparable data on increasing infection after birth in never-breast-fed
infants may be found in Coutsoudis and others (1999, table 2).
What can this mean? One possibility is that the infants who supposedly were
not breast-fed actually were breast-fed. In the Kenya study, infants who were
mixed feeders (some breast-feeding and some formula) were supposed to be
placed with the breast-feeding cohort (Nduati et al. 2000; Kent 2002). Though
that was the intent, about 25 percent of the women who were assigned to the
formula feeding group were reported to have also been given breast milk (Coova-
dia and Coutsoudis 2001). This could account for infection of some infants after
birth.
Another possibility is that there is a latency e’ect. It may be that when the ac-
tual transmission of the virus occurs during pregnancy or delivery, the resulting
biological activity does not rise to the level of detectability until some weeks or
months after birth. If this is the case, the share of mother-to-child transmission
attributable to breast-feeding might be much lower than has been supposed. Ac-
cording to this table, at six months the rate of hiv infection for breast-fed infants
feeding infants of hiv-positive mothers 179
in South Africa was only 4.8 percent higher than the rate for formula-fed infants.
Because there might well be a significant time-lag between transmission of the
virus and the onset of measurable infection, there is no good way to know the ex-
act moment of transmission, and thus no good way to determine which infec-
tions are due specifically to breast-feeding.
It is important to distinguish between transmission and infection. As we see
in table 12.1, the onset of infection can appear several months after birth, even for
cases in which there is no breast-feeding. The most plausible explanation is what
we can call a latency e’ect: The virus was transmitted before birth, but the infec-
tion did not rise to a detectable level until several months after birth.
There are ambiguities regarding the very meaning of hiv infection. The ter-
minology that emphasizes virus transmission suggests that if a small number
of copies of the virus pass from mother to infant, that infant is thereby infected,
by definition. However, some analysts emphasize the importance of serocon-
version, the change in the blood stream that can result from the activity of the
virus. Transmission is instantaneous, but seroconversion, the process of infec-
tion, apparently can take weeks or even months. The evidence of seroconversion
is the presence of antibodies in the bloodstream. It is important to distinguish
infection in the first sense (presence of the virus) from infection in the second
sense (seroconversion), because the first does not always lead to the second.
Coovadia and Coutsoudis (2001, 5) say the only data that we have currently
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