It is estimated that three-quarters of all patients undergoing solid organ transplantation experience new infection or reactivation of latent cytomegalovirus (CMV). In all transplant types, seronegative recipients of organs from seropositive donors (D+/R-) are at the highest risk to develop CMV infection and more serious disease. The American Society of Transplantation standardized diagnostic criteria for CMV infection and disease are presented below: 1. CMV infection: isolation of virus, viral protein or nucleic acid from any tissue or body fluid; primary infection - emergence of CMV or CMV specific antibodies in untreated patients previously CMV seronegative, recurrent infection - new infection in patients with previous history, but without evidence of infection over >1 month of active surveillance. 2. CMV syndrome: CMV in the blood, plus >1 of the following: 1) fever >38°C (>2 days), 2) thrombocytopenia, leucopenia, or anemia, 3) worsening/ new malaise, 4) transaminase increases in non liver transplant recipients. 3. CMV disease: isolation of virus, or evidence of viral replication in the presence of clinical symptoms of organ specific disease (end- organ disease) such as pneumonia, gastrointestinal disease, hepatitis, central nervous system disease, nephritis, cystitis, myocarditis and retinitis. Current antiviral agents and preventive strategies have led to a decrease in incidence of CMV disease. Compared to patients treated with no viral therapy, those receiving preemptive therapy and prophylaxis have a 72-80% lower likelihood for the development of CMV disease. Futhermore, reduced allograft rejection, opportunistic infections and mortality has been documented with the receipt of prophylaxis. Although prophylaxis has effectively prevented early CMV disease, the incidence of late-onset CMV disease occurring after discontinuation of prophylaxis has increased from 0-5% in the era of long-term use of acyclovir to 2.6-7% in patients receiving prophylaxis with oral ganciclovir. Valganciclovir has emerged as the preffered antiviral agent for prevention of CMV in solid-organ recipients because of its oral availability, convenient dosing schedule, and 10-fold oral bioavailability then oral ganciclovir. Evidence-based systematic synthesis data show that overall incidence of CMV disease in patients receiving valganciclovir prophylaxis was 9.9% and 2.6% in preemptive therapy group. The overall rejection rate of 10.8% was in patients receiving preemptive therapy and 17.6% in prophylactic studies. In preemptive therapy group 3.9% patients had graft loss. Prophylactic studies described the number of patients with graft loss, and the overall rate was 2.5%. Opportunistic infections developed 28.5% in preemptive therapy groups and 7.8% in prophylactic studies. The overall mortality rate was 8.2% from preemptive studies and 4.4% from prophylactic groups. Both prophylaxis and preemptive strategies are effective for CMV disease prevention. The peak incidence of CMV disease has shifted from

Keywords: CMV infections, Organ Transplantation, Cytomegalovirus