enzyme analyses of CMV DNA have been used to demonstrate route of transmission of the virus in situations in which close contact occurs, such as breast-feeding, sexual activity, day care, and interaction between parents or caretakers and infected toddlers.
The prevalence of CMV infection increases with age, but, according to geographic, ethnic, and socioeconomic backgrounds, the patterns of acquisition of this infection vary widely among populations (6). As illustrated in Figure 1, CMV is acquired earlier in life in developing countries and among the lower socioeconomic strata of developed countries. Differences between populations can be particularly striking during childhood. Presumably, these significant differences are the reflection of factors that account for increased exposure to CMV such as crowding, breast-feeding, sexual practices, and certain rearing practices.
Studies carried out in the past 15 years indicate that breast-feeding and child-rearing practices singly or in combination are two of the most powerful factors influencing the rate of acquisition of CMV in the various populations (7, 8). Breast-feeding is the major factor during the first year of life with CMV excretion rates of >50% observed in countries where the majority of women are seropositive and breast-feed their infants. The rapid increase in the rate of infection that generally takes place after the first year of life is the result of close contact and exposure to children who acquired CMV infection from a maternal source (i.e., in utero, from exposure to genital secretions at birth, or from breast milk). In our view, the profound alterations that have occurred in breast-feeding