Yu 2011a.

Methods	Multicentre retrospective cohort study
Participants	Country: China (Zhengzhou city) Setting: ICU Number of sites: 4 Number of individuals: 128 Inclusion criteria: not recorded Influenza type: 2009 influenza A H1N1 virus (H1N1pdm09) Mean (SD) age (years): males 28.5 (16.4); females 28.5 (20.4), range 8 months to 79 years Male sex: 77 (60.2%) Comorbid illness: not recorded Disease severity: not recorded
Interventions	Groups: CS (n = 54) versus no CS (n = 74) No details on types and doses of CS Duration of treatment in days: mean (SD): died 8.3 (8.0); survived 2.6 (4.2)
Outcomes	Mortality (time point not recorded). Raw data presented without unadjusted or adjusted odds ratio estimates.
Risk of bias (Newcastle‐Ottawa Scale)	Selection domain score (max 4): 2 Comparability domain score (max 2): 1 Outcome domain score (max 3): 1
Notes	In Chinese language. Study of risk factors for mortality

APACHE: Acute Physiology and Chronic Health Evaluation
 ARDS: adult respiratory distress syndrome
 CI: confidence interval

 COPD: chronic obstructive pulmonary disease

 CS: corticosteroid
 
ICU: intensive care unit
 
IQR: interquartile range
 NAI: neuraminidase inhibitor
 PaO₂/FiO₂: ratio of partial pressure of oxygen in arterial blood to inspired fraction of oxygen
 PCR: polymerase chain reaction

 RT‐PCR: reverse transcription‐polymerase chain reaction

 SAPS: Simplified Acute Physiology Score

 SD: standard deviation
 
SOFA: Sequential Organ Failure Assessment