Changes in the Epidemiology of Cytomegalovirus

Abstract

Human cytomegalovirus (CMV) is highly species-specific, and humans are believed to be its only reservoir (1). Seroepidemiologic surveys have found CMV infection in every population that has been tested, including remote Indian tribes in the Amazon basin that lacked evidence of past measles or influenza infections (2, 3). CMV infection is endemic and without seasonal variation. Climate does not affect the prevalence of infection, and there are no known vectors in the natural transmission cycle. 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 (4). As illustrated in figure 1, in general, 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, with rates of seropositivity of 4–6-yr-olds varying from less than 10% in Great Britain and certain populations in the United States to nearly 100% in Africa and the South Pacific. 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. Transmission occurs by direct or indirect person-to-person contact. Sources of the virus include urine, oropharyngeal secretions, cervical and vaginal secretions, semen, milk, tears, and blood (5, 6). CMV is not very contagious, and the spread of infection requires close or intimate contact with infected secretions. Restriction-enzyme analyses of CMV DNA have been used to demonstrate person-to-person spread of the virus in situations where close contact occurs, such as breast-feeding, sexual activity, day care, and interaction between parents or care takers and infected toddlers. Under special circumstances fomites may also play a role, since CMV has been shown to retain infectivity for hours on plastic surfaces and has been isolated from randomly selected toys and surfaces in day-care centers (7, 8).