Since then, CMV has become recognized as a nearly ubiquitous virus that plays an important role in many diseases, including a form of mononucleosis and disseminated disease in the immunocompromised host. CMV is shed in semen, cervical secretions, saliva, maternal milk, and urine. In late adolescence and adulthood, genital transmission is common. Primary infection in pregnant women may result in transplacental spread to the fetus, sometimes with devastating consequences. Approximately one percent of newborns in developed countries are infected with CMV, and the incidence is much higher in developing areas.
Perinatal infection is also common because of spread from maternal milk or other secretions.
Communal living and poor personal hygiene facilitate transmission. Blood transfusions and organ transplantation may also transmit CMV from an asymptomatic donor to a recipient. Once infected, individuals probably carry the virus for life. Generally, such infections remain dormant, but reactivation occurs during periods of immune compromise. Reinfections with new strains of CMV can also occur in immunosuppressed patients.