Surprise CMV infection is more prevalent in children than in parents

A 1982 study of CMV infections in a day-care center that served a population comprised mostly of middle-income families with college-educated parents found that the prevalence of CMV infection in the pre-schoolers attending the center was higher than in their parents, and there were numerous examples of toddlers who were shedding CMV and whose mothers had never had CMV infection (Pass et al, 1982). This paradox in related prevalence of CMV infection suggested that horizontal transmission between children was occurring, and also that widespread use of day-care centers could change the epidemiology of CMV infection in the US.

Subsequent studies in day-care centers confirmed horizontal transmission of CMV from young children, and raised concerns about transmission of CMV from children to their mothers or day-care workers. Further evidence of transmission of CMV from child to child came from a cohort study of children in day care which showed that only around 10 percent of children less than one year of age had CMV, and that the majority of children acquired CMV during their second year of life (Pass et al, 1984). In one day-care center, 100 percent of children in a class group of children aged 1-2 years were shedding CMV This pattern of infection was incompatible with a maternal source but was compatible with horizontal transmission during the second year of life, when ambulatory toddlers have frequent opportunities for contact with each other and for sharing of toys - which are often mouthed by children of this age. Studies that tracked transmission of CMV by comparing restriction fragment length polymorphism (RFLP) of DNA ("DNA fingerprinting") from CMV strains isolated from children in day-care centers confirmed horizontal transmission of virus between children (Adler, 1985).

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