HHV-6 infection has been frequently observed in critically ill patients [12, 15] . In one study, HHV-6 infection occurred in 53.5% of all patients (54/101) requiring hospitalization in the ICU as compared with none of the healthy volunteers [15] . In another study, HHV-6 infection occurred in 54% of all ICU patients with at least two organ failures as opposed to 15% of those with less than two organ failures [12] . HHV-6 viremia was assessed by the PCR assay at a mean of day 4 and day 1.8, respectively [12, 15] . Potential association between CMV and HHV-6 infection could not be assessed because only one patient developed CMV infection in each study. Both studies failed to show an association between HHV-6 infection and mortality. HHV-7 infection was observed more commonly in healthy volunteers (18/50, 36%) as compared with ICU patients (14/101, 14%; P = 0.002) in one study [15] .