Jain 2009.

Methods	Multicentre retrospective cohort
Participants	Country: USA Setting: in‐hospital Number of sites: national surveillance data Number of individuals: 272 (CS data available for 239) Inclusion criteria: individuals hospitalised with influenza‐like illness Definition of influenza: laboratory confirmed Influenza type: 2009 influenza A H1N1 virus (H1N1pdm09) Median age (years): cohort 21 years (IQR 21 days to 86 years) Male sex: not reported for individual groups Comorbid illnesses: not reported for individual groups Disease severity: not reported for individual groups
Interventions	Groups: no CS (n = 153); CS (n = 86) Type: not reported Co‐interventions: antivirals 200/268 (74.6); antibiotics 206/260 (79.2)
Outcomes	Death/ICU admission versus survival/no ICU admission
Risk of bias (Newcastle‐Ottawa Scale)	Death/ICU admission versus survival/no ICU admission Selection domain score (max 4): Comparability domain score (max 2): 0 Outcome domain score (max 3): 3
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