Exposure to cytomegalovirus (CMV) occurs throughout life and by adulthood. 50-90% of the population is seropositive for CMV antibodies. CMV is spread by close contact, sexula transmission, perinatal or congenital transmission, and through blood transfusions and tissue transplants. Intrauterine or congenital infections occur in 0.5 to 2.2% of all live births. Symptomatic congenital infections usually occur in infants born to nonimmune mother who have primary infections during pregnancy. Latency and reactivation of CMV influence the interpretation of serological results. A single positive CMV IgG results is an indication of present or past infection. The presence of CMV IgM suggests a recent CMV exposure but does not differentiate between primary infection and reactivation.