Most infections with CMV go undiagnosed, as the virus usually produces few, if any, symptoms and tends to reactivate intermittently without symptoms. Persons who have been infected with CMV develop antibodies to the virus, which persist in the body for the lifetime of that individual. A number of laboratory tests that detect these antibodies to CMV have been developed to determine if infection has occurred and are widely available from commercial laboratories. In addition, the virus can be cultured from specimens obtained from urine, throat swabs, bronchial lavages and tissue samples to detect active infection. Both qualitative and quantitative polymerase chain reaction (PCR) testing for CMV are available as well, allowing physicians to monitor the viral load of people infected with CMV.