Epidemiology and transmission
CMV is a member of theHerpesviridaefamily and is one of the 8 herpesviruses to cause human infection (Table 1). CMV is acquired through contact with infected bodily fluids, and like the other herpesviruses, CMV remains permanently within its host, with periods of latency and activation throughout the person’s life span.5
In more than 95% of cases, CMV enters the immunocompetent host without causing any symptoms of infection, as it has developed numerous gene products that will evade or interfere with the immune response.5
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Once infected, the person develops an extensive immune response that involves all arms of the human adaptive immune system, making vertical transmission less common in previously infected mothers.6However, when the woman is infected for the first time during pregnancy, the virus can be vertically transmitted to the fetus through the placenta, resulting in detrimental effects for the newborn.3
Up to 90% of the U.S. population will be infected with CMV by age 80 years.3Yet approximately 30% to 50% of women of childbearing age have never been infected with CMV, and up to 4% of them will develop their first (primary) CMV infection during pregnancy.7Within that group of women, 30% to 40% will transfer the infection to the fetus through the placenta.3
Mothers who had an earlier CMV infection and experience a period of reactivation during pregnancy or become infected with a new strain of the virus have about a 1% risk of transmitting the virus to the fetus.3
Following in utero transmission, CMV causes more cases of congenital illness and disease than do the 29 currently recommended conditions for which newborns are screened in the United States.6
