We included studies in which: critically ill immunocompetent adults were monitored either retrospectively or prospectively for the development of CMV infection in the ICU and; the rate of CMV infection was explicitly reported. CMV infection was defined as evidence of positive viral cultures, antigenemia, and/or DNAemia by PCR from blood or a clinical specimen. Patients were considered to be immunocompetent if they were not solid organ or hematopoietic stem cell transplant recipients, not infected with HIV, did not have primary immunodeficiencies, and were not recipients of immunosuppressive agents such as calcineurin-inhibitors, anti-TNF- drugs, antilymphocyte antibodies, or chemotherapeutic agents for treating cancer. We excluded studies in which an increase in CMV serologic titers in the absence of viremia was the sole evidence for CMV infection.