Two of the authors independently searched articles and extracted the following data for analyses: study design, inclusion criteria, type and frequency of CMV assays, rate of CMV infection, rate of CMV IgG positivity, the time elapsed from ICU admission to CMV infection, risk factors for CMV infection, and outcomes (i.e. mortality, duration of ICU stay). Any discrepancies were resolved by review and discussion. Authors of published studies were contacted if reported data required further clarification. Additional mortality data was provided in one study [12] .