Populations at risk for severe or complicated influenza illness: systematic review and meta-analysis

To evaluate risk factors for severe outcomes in patients with seasonal and pandemic influenza.

Systematic review. STUDY SELECTION: Observational studies reporting on risk factor-outcome combinations of interest in participants with influenza. Outcomes included death, ventilator support, admission to hospital, admission to an intensive care unit, pneumonia, and composite outcomes. DATA SOURCES: Medline, Embase, CINAHL, Global Health, and the Cochrane Central Register of Controlled Trials to March 2011. RISK OF BIAS ASSESSMENT: Newcastle-Ottawa scale to assess the risk of bias. GRADE framework to evaluate the quality of evidence.