title: Populations at risk for severe or complicated Avian Influenza H5N1: a systematic review and meta-analysis.
abstract: BACKGROUND
  Little is known about risk factors for severe outcomes in patients infected with H5N1 and no systematic review has been conducted. Understanding risk factors is an important step for prioritizing prophylaxis or treatment in the event of a pandemic.
  
  
  OBJECTIVE
  To systematically evaluate risk factors for severe outcomes in patients with avian influenza H5N1 infection.
  
  
  METHODS
  MEDLINE, EMBASE, CINAHL, GlobalHealth, and CENTRAL through March 2011.
  
  
  METHODS
  Observational studies of any design published in English, French, Spanish, German or Korean that reported on risk factor-outcome combinations of interest in participants with confirmed H5N1 infections. Outcomes considered included death, ventilator support, hospital and ICU admission, pneumonia, and composite outcomes.
  
  
  METHODS
  Risk of bias was assessed using the Newcastle-Ottawa scale (NOS).
  
  
  RESULTS
  We identified 20 studies reporting on 999 patients infected with H5N1. The majority of studies (n = 14, 70%) were at intermediate risk of bias, i.e. 4-6 points on the NOS. Females were at increased risk of death (OR 1.75, 95% CI 1.27-2.44), while young age, in particular <5 years of age (OR 0.44, 95% CI 0.25-0.79 for death), was protective. Data on traditional risk factors was scarce and requires further studies. Another major limitation in the published literature was lack of adjustment for confounders.
  
  
  CONCLUSIONS
  Females were at increased risk for complications following H5N1 infection while young age protected against severe outcomes. Research on traditional risk factors was limited and is required.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ontario, Canada; Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada; Michael G. DeGroote Institute for Infectious Diseases Research, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Dominik
authors.initials: D
authors.lastname: Mertz
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada; Division of Infectious Diseases, Departments of Internal Medicine, Soon Chun Hyang University Seoul Hospital, Seoul, Republic of Korea.
authors.forename: Tae Hyong
authors.initials: TH
authors.lastname: Kim
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Jennie
authors.initials: J
authors.lastname: Johnstone
authors.affiliation: Department of Microbiology, Mount Sinai Hospital, Toronto, Ontario, Canada; Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Po-Po
authors.initials: PP
authors.lastname: Lam
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada; Division of Infectious Diseases, Department of Pediatrics, The Hospital for Sick Children, University of Toronto, Ontario, Canada.
authors.forename: Michelle
authors.initials: M
authors.lastname: Science
authors.affiliation: Department of Microbiology, Mount Sinai Hospital, Toronto, Ontario, Canada; Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland.
authors.forename: Stefan P
authors.initials: SP
authors.lastname: Kuster
authors.affiliation: Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Shaza A
authors.initials: SA
authors.lastname: Fadel
authors.affiliation: Division of Infectious Diseases, Department of Pediatrics, The Hospital for Sick Children, University of Toronto, Ontario, Canada.
authors.forename: Dat
authors.initials: D
authors.lastname: Tran
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Fernandez
authors.affiliation: Health Sciences Library, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Neera
authors.initials: N
authors.lastname: Bhatnagar
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ontario, Canada; Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, Ontario, Canada; Michael G. DeGroote Institute for Infectious Diseases Research, McMaster University, Hamilton, Ontario, Canada; Department of Pathology and Molecular Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Loeb
mesh_terms: D000818:Animals; D001717:Birds; D005260:Female; D054884:Host-Pathogen Interactions; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000502:physiology*; D005585:Influenza in Birds / Q000821:virology*; D007251:Influenza, Human / Q000821:virology*; D012307:Risk Factors; D012737:Sex Factors