Next, studies were categorized based on the frequency of virologic monitoring because it can influence the rate of CMV infection. In five studies in which CMV infection was monitored at least weekly, the rate of CMV infection ranged from 6 to 33% with the median of 32% [7, 8, 10, 11, 16] . In contrast, CMV infection rate was 0.8 to 2.1% in two studies in which assessment for CMV infection was performed only once, 1.8 to 4 days after ICU admission [12, 15] .