CMV infection rate was 0.8 to 2.1% in two studies where the PCR assay was performed only once at a mean of 1.8 and 4 days following the onset of illness requiring ICU admission [12, 15] . The median time to first detectable CMV viremia was 12 days (range 3 to 57 days) in a study where the PCR assay was performed thrice weekly [11] . Thus, it appears that CMV infection is a rare event very early in the course of critically ill patients and that most infections develop between 4 and 12 days after the onset of illness requiring ICU stay, which could lead to a hypothesis that CMV infection may coincide with the development of compensatory anti-inflammatory response syndrome, and not with the initial surge of pro-inflammatory cytokines.