Weaning age: a critical period
Breast milk is a nutritious and generally safe food
for newborn infants, and exclusive breast-feeding,
i.e., giving the infant no fluid or food other than
breast milk, protects against diarrhoea by minimizing
the infant's exposure to foodbome and waterbome
pathogens. Breast-feeding may also reduce the severity
of diarrhoeal illnesses and has an influential
effect on preventing diarrhoea-associated deaths
(4-6). However, when the infant reaches 4-6 months
of age, breast milk needs to be supplemented, and
later on (>2 years of age) substituted by appropriate
foods until the child is gradually introduced to family
food. With the introduction of weaning foods,
which in many countries are prepared under unhygienic
conditions, infants who until then have only
consumed breast milk may be exposed to infective
doses of foodbome pathogens. Many studies report
that the incidence of diarrhoeal diseases is especially
high after weaning is initiated (7). In a study of
infants and children in a Guatemalan Mayan village,
Mata noted that the prevalence of many infections
increased during the weaning period (8). Rowland &
McCollum reported that there is particularly high
incidence of diarrhoeal diseases between 7 and 18
months with a peak at 9 months of age (9). Similarly,
Black et al. found that the prevalence of diarrhoea
was highest during the second 6 months of life (10,
11) and declined with increasing age thereafter. The
declining incidence of foodborne illnesses with
increasing age is explained by the probable acquisition
of immunity from repeated exposure to the
pathogens. A review by Snyder & Merson indicated
that the median incidence of diarrhoeal diseases was
three-to-six episodes per year, the highest incidence
being during the second half of infancy (12).
For various reasons, weaning is initiated in
many cultures at an even earlier age than is nutritionally
necessary, i.e., 4-6 months of age. Recent
surveys indicate that exclusive breast-feeding is a
very infrequent practice, and water, various infusions,
rice water, and similar foods are often introduced to
young infants at a very early age.d Consequently,
contaminated weaning food may increase the risk of diarrhoeal diseases even during the very early
months of life.