Diagnosis of Cytomegalovirus Infection

Diagnostic procedures for documenting cytomegalovirus (CMV) infection include culture, cytology, serology, and the detection of CMV antigens and/or nucleic acids within infected tissues. Each procedure is useful, but each has specific pitfalls. A positive urine, blood, or genital culture confirms CMV infection but does not prove that CMV is causing a specific clinical syndrome, since excretion of virus may continue for months to years following primary infection and may reoccur when a patient is immunocompromised. Seroconversion from negative to positive for specific IgG antibody is usually diagnostic of primary infection but does not provide a rapid diagnosis. CMV-specific IgM antibody is associated with primary CMV infection in nonimmunocompromised patients but may be present in immunocompromised (e.g., AIDS) patients who are infected by but do not have disease due to CMV. Conversely, tests for IgM may be negative in immunocompromised patients or neonates who are actively infected and may be falsely positive in infants who are not congenitally infected. Lastly, detection of CMV antigen in tissue by monoclonal antibodies or of CMV nucleic acids by genetic probes helps confirm tissue infection. Demonstration of CMV inclusions by cytologic or histologic examination is diagnostic of infection, but this method is not sensitive.