HSCT recipients are closely followed for EBV infection in the post-transplant period. Although most of the blood product transfusions occur during the peri-transplant period, it is possible that patients receive blood products at a later time post-transplantation. Follow-up on EBV PCR results and complications related to EBV will therefore continue up to one year post-transplant (or time of death). This time window will allow documentation of the entire clinical trajectory of HSCT. Protocols for follow-up after transplant, and for the diagnosis and treatment of EBV disease in allogeneic graft recipients have been reviewed in all participating sites. The incidence of EBV infection in recipients is measured by quantitative real-time PCR testing performed AT MINIMUM every 1-2 weeks from the time of transplant until hospital discharge (which is usually around 6 weeks post-transplantation). After hospital discharge, EBV PCR monitoring is performed at every clinical follow-up visit: AT LEAST twice per month for approximately 4-6 months post-transplant or as long as the patient remains immune suppressed. Thereafter, approximately one EBV PCR per month is performed until 1-year post-transplant.