title: When should a diagnosis of influenza be considered in adults requiring intensive care unit admission? Results of population-based active surveillance in Toronto.
abstract: BACKGROUND
  There is a paucity of data about the clinical characteristics that help identify patients at high risk of influenza infection upon ICU admission. We aimed to identify predictors of influenza infection in patients admitted to ICUs during the 2007/2008 and 2008/2009 influenza seasons and the second wave of the 2009 H1N1 influenza pandemic as well as to identify populations with increased likelihood of seasonal and pandemic 2009 influenza (pH1N1) infection.
  
  
  METHODS
  Six Toronto acute care hospitals participated in active surveillance for laboratory-confirmed influenza requiring ICU admission during periods of influenza activity from 2007 to 2009. Nasopharyngeal swabs were obtained from patients who presented to our hospitals with acute respiratory or cardiac illness or febrile illness without a clear nonrespiratory aetiology. Predictors of influenza were assessed by multivariable logistic regression analysis and the likelihood of influenza in different populations was calculated.
  
  
  RESULTS
  In 5,482 patients, 126 (2.3%) were found to have influenza. Admission temperature ≥38°C (odds ratio (OR) 4.7 for pH1N1, 2.3 for seasonal influenza) and admission diagnosis of pneumonia or respiratory infection (OR 7.3 for pH1N1, 4.2 for seasonal influenza) were independent predictors for influenza. During the peak weeks of influenza seasons, 17% of afebrile patients and 27% of febrile patients with pneumonia or respiratory infection had influenza. During the second wave of the 2009 pandemic, 26% of afebrile patients and 70% of febrile patients with pneumonia or respiratory infection had influenza.
  
  
  CONCLUSIONS
  The findings of our study may assist clinicians in decision making regarding optimal management of adult patients admitted to ICUs during future influenza seasons. Influenza testing, empiric antiviral therapy and empiric infection control precautions should be considered in those patients who are admitted during influenza season with a diagnosis of pneumonia or respiratory infection and are either febrile or admitted during weeks of peak influenza activity.
authors.affiliation: Mount Sinai Hospital, 600 University Avenue, Toronto, ON M5G 1X5, Canada.
authors.forename: Stefan P
authors.initials: SP
authors.lastname: Kuster
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Katz
authors.forename: Joanne
authors.initials: J
authors.lastname: Blair
authors.forename: James
authors.initials: J
authors.lastname: Downey
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Drews
authors.forename: Sandy
authors.initials: S
authors.lastname: Finkelstein
authors.forename: Rob
authors.initials: R
authors.lastname: Fowler
authors.forename: Karen
authors.initials: K
authors.lastname: Green
authors.forename: Jonathan
authors.initials: J
authors.lastname: Gubbay
authors.forename: Kazi
authors.initials: K
authors.lastname: Hassan
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Lapinsky
authors.forename: Tony
authors.initials: T
authors.lastname: Mazzulli
authors.forename: Donna
authors.initials: D
authors.lastname: McRitchie
authors.forename: Janos
authors.initials: J
authors.lastname: Pataki
authors.forename: Agron
authors.initials: A
authors.lastname: Plevneshi
authors.forename: Jeff
authors.initials: J
authors.lastname: Powis
authors.forename: David
authors.initials: D
authors.lastname: Rose
authors.forename: Alicia
authors.initials: A
authors.lastname: Sarabia
authors.forename: Carmine
authors.initials: C
authors.lastname: Simone
authors.forename: Andrew
authors.initials: A
authors.lastname: Simor
authors.forename: Allison
authors.initials: A
authors.lastname: McGeer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003657:Decision Making; D005260:Female; D006786:Hospitals, Urban; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification; D009980:Influenza A virus / Q000302:isolation & purification; D009981:Influenza B virus / Q000302:isolation & purification; D007251:Influenza, Human / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology / Q000821:virology; D007362:Intensive Care Units; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D010343:Patient Admission; D011159:Population Surveillance; D055815:Young Adult