Candidate variables assessed as predictors for CMV infection varied for different studies and primarily included demographic and clinical characteristics, and severity of illness markers. Age did not appear to be a risk factor for CMV infection [7, 8, 10, 11, 13, 16, 18] and the association between CMV infection and gender was inconsistent [7, 8, 10, 11, 13, 16, 18] . Other risk factors identified included mechanical ventilation at admission (odds ratio [OR] 8.5, 95% confidence interval [CI] 1.1 to 66.5 for high-grade CMV viremia, i.e. CMV PCR > 1000 copies/ml) [11] , bacterial pneumonia [8] , and sepsis (OR 4.62, P = 0.02) [10] . Corticosteroid use was a risk factor in one study [8] . In a retrospective case-control study where variables used in a multivariate logistic regression model were not clearly documented, neither corticosteroid use nor sepsis was a risk factor for CMV infection [18] . Transfusion within 24 hours of admission was associated with high-grade viremia, i.e. CMV viral load greater than 1000 copies/ml (OR 6.7, 95% CI 1.1 to 42.7) [11] ; however, no association between CMV infection and transfusion during hospitalization was documented in two other studies [18] . The mean number of packed red blood cell transfusion was larger in patients with CMV infection than in those without it (22.3 units vs. 11.2 units, P = 0.002); however, this difference was not statistically significant after controlling for other risk factors [8] . Malignancy was not associated with CMV infection [9, 10, 18] . None of the disease severity scores including Acute Physiology and Chronic Health Evaluation (APACHE) II score [7, 8, 11, 13] , sepsisrelated organ failure assessment (SOFA) score [16] , or SAPS II [10, 18] correlated with a risk of CMV infection.