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Description of the Pathogen

Human cytomegalovirus, a member of the herpesvirus group, consists of double-stranded DNA inside an icosahedral capsid made up of 162 capsomeres. The capsid is surrounded by a lipid-containing envelope. These virus particles are large and complex; analysis of their antigenic structure has just begun. Neither the number of strains nor the significance of their antigenic differences is known (Gold and Nankervis, 1982).

Host Immune Response

The normal immunocompetent host develops both humoral and cell-mediated immune reponses to primary cytomegalovirus infection (Gold and Nankervis, 1982). Despite these responses, virus shedding can persist for weeks or months, often followed by latent infection. Periodic reactivation of infection usually is asymptomatic, but may cause extensive disease in the immunocompromised host. Interstitial pneumonia is the most serious manifestation in these individuals, and is usually associated with fever. Infections of the liver, the gastrointestinal tract, and the retina also are observed in immunocompromised hosts.

Magnitude of Disease Burden

The following groups are those primarily at risk: (a) fetuses subject to congenital infection; (b) infants subject to perinatal infection; (c) recipients of multiple transfusions of whole blood; (d) recipients of organ and bone marrow transplants; (e) persons with leukemia; and (f) normal adults who may contract CMV mononucleosis or other febrile illnesses. Some of these groups overlap; however, because of the lack of data on the extent of overlap the committee chose to consider them separately in the disease burden estimates.

Congenital Cytomegalovirus Infection

CMV infection occurs in an estimated 0.4 to 2.3 percent of live births in the United States (Alford, personal communication, 1983; Lang, 1980; Plotkin, personal communication, 1983; Plotkin et al., 1983; Stagno et al., 1983). To simplify this analysis, the following calculations are based on an estimate of 1 percent or 37,883 infected infants. Most infected infants are asymptomatic at birth, but late sensorineural sequelae may occur.

Infants Symptomatic at Birth An estimated 7.5 percent (2,841) of congenitally infected infants are symptomatic at birth (see Tables E.1 and E.2). Symptoms of cytomegalic inclusion disease (CID) include

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