Monitoring transplant patients for human cytomegalovirus: Diagnostic update

Human cytomegalovirus (HCMV) infections are the major viral complications associated with the post-transplant period in haematopoietic stem cell and solid organ transplant recipients. HCMV infection may be systemic (high viral load in blood associated with fever, leucopenia and thrombocytopenia) or local (clinical symptoms of viral infection within a single organ [e.g. lungs] or apparatus [gastrointestinal tract]). Both infection types can be associated with each other. Systemic HCMV infections are diagnosed by performing antigenaemia or DNAemia assay (polymerase chain reaction [PCR]) on blood samples: both assays are quantitative. Local infections are diagnosed by virus isolation from tissue biopsies or secretions, or by PCR. To prevent HCMV disease, a prophylactic approach is usual in the USA, while a pre-emptive (presymptomatic) approach, which is more common in Europe, involves administering antivirals when a predetermined viral load is reached in blood. Simultaneous virological and immunological follow-up is the best approach to efficient monitoring of HCMV infections in transplant recipients. Lack of immune reconstitution entails repeated episodes of recurrent infection with multiple courses of antiviral treatment, whereas reconstitution of both arms of the HCMV-specific T-cell mediated immune response controls HCMV infection. The exception is for cases of graft rejection or graft versus host disease treated with steroids or antilymphocyte globulin, which require virological monitoring and (in some cases) antiviral treatment until resolution of the adverse event.