Cytomegalovirus (CMV) disease is an important cause of morbidity in solid organ transplantation recipients and remains the most common opportunistic viral infection in these patients. Standard CMV prevention strategies include universal prophylaxis and pre-emptive therapy with viral load monitoring. However, neither of these strategies has been successful in eliminating CMV disease as seen by high rates of viremia, incidence, and CMV recurrence despite treatment. Recently, the Quantiferon-CMV assay has been shown to predict late CMV reactivation after prophylaxis and to be predictive of viral progression and the need for antiviral therapy in organ transplant recipients who develop low level CMV viremia. The purpose of the current study is to test the clinical strategy of using the Quantiferon-CMV assay in guiding the duration of primary CMV prophylaxis in solid organ transplant patients.