A key question is whether CMV infection adversely affects outcomes in critically ill patients. Virtually all studies have documented that CMV infection was related to prolonged mechanical ventilation and duration of ICU stay in patients with CMV infection. CMV infection has also been associated with organ system failure and at least two studies have documented significantly higher mortality rates in patients with CMV infection compared with those without it [9, 18] . Thus, although these data do not prove a causal association as CMV infection may have been more likely to develop or diagnosed in sicker patients, existing evidence suggests that CMV infection is associated with poor outcomes even in immunocompetent critically ill patients. We believe that a causal association between these can only be assessed by carefully conducted clinical trials designed to show whether suppression of CMV has a mitigating effect on the severity of illness.