Cytomegalovirus (CMV), a human-restricted betaherpesvirus, infects nearly half the U.S. population. CMV prevalence differs widely according to age, socioeconomic status, sexual activity, and race ethnicity. Over 90% of the overall U.S. population is infected by 80 years of age, and an estimated one-half million women of childbearing age are infected each year. Congenital CMV infection involves approximately 1% of all newborns and is the leading infectious cause of birth defects.

CMV infection is lifelong and usually asymptomatic, even as virus is shed into secretions. Primary CMV infection occasionally results in self-limiting acute illness (eg, heterophile-negative mononucleosis, viral syndrome, or hepatitis) and very rarely causes protracted or severe disease in otherwise healthy persons. Primary CMV infection of women during pregnancy increases risk of symptomatic congenital CMV infection. Approximately 8000 of the ˜35 000 congenitally CMV-infected babies born each year in the United States have sequelea, including hearing loss, vision loss, mental retardation, or death. Persons with profound cellular immune deficiency, such as accompanies acquired immunodeficiency syndrome (AIDS) and hematopoietic stem cell or solid organ transplantation, are predisposed to debilitating or life-threatening CMV disease resulting from primary, reactivation, or recurrent infection. CMV causes a broad spectrum of disease, and the leading clinical manifestations vary among the different patient types but commonly include retinitis, gastrointestinal disease, hepatitis, pneumonitis, or encephalitis. Unrestrained CMV replication can directly damage a variety of organs and tissues and have immunomodulatory effects that are indirectly linked to sequelae of allograft dysfunction or rejection, superinfections with opportunistic pathogens, posttransplant lymphoproliferative disorder, and decrease in survival of human immunodeficiency virus (HIV)-positive persons living in the era of highly active antiretroviral therapy.