title: Predictors of pandemic influenza infection in adults presenting to two urban emergency departments, Toronto, 2009.
abstract: OBJECTIVE
  Identifying features that differentiate patients with H1N1 influenza infection from those with other conditions may assist clinical decision making during waves of pandemic influenza activity.
  
  
  METHODS
  From April 27 to June 15, 2009, nasopharyngeal swabs were obtained from all adults presenting to two urban emergency departments (EDs) with illness including fever or respiratory symptoms. H1N1 infection was detected by reverse transcriptase-polymerase chain reaction. Chart review was performed to compare cases of H1N1 influenza (n  =  117) to matched controls.
  
  
  RESULTS
  The median age of cases was 35 years versus 50 years for controls (p < .001). In those with pre-existing conditions, asthma was present in 31% of cases versus 14% of controls (OR 2.6, 95% CI 1.3-5.4). Cough (OR 7.8, 95% CI 3.2-19), fever (OR 3.0, 95% CI 1.7-5.4), headache (OR 2.0, 95% CI 1.2-3.2), and myalgias (OR 1.9, 95% CI 1.2-3.1) were significantly more common in H1N1 cases. The median white blood cell count was 5.7 × 109/mL versus 10.9 × 109/mL (p < .001). The combination of fever and cough had an OR of 5.3. Fever, cough, low white blood cell (WBC) count, and tachycardia had the highest OR at 11. The absence of both fever and cough had a negative predictive value of 99%, but this occurred in only 8% of controls.
  
  
  CONCLUSIONS
  In patients presenting to the ED, the combination of fever, cough, tachycardia, and WBC count < 10 × 109/mL was suggestive of H1N1 influenza infection. However, clinical features could not reliably distinguish influenza from other acute respiratory illnesses in adult ED patients.
authors.affiliation: Division of Infectious Diseases, University of Toronto. Toronto, Canada. todd.lee@utoronto.ca
authors.forename: Todd C
authors.initials: TC
authors.lastname: Lee
authors.forename: Linda R
authors.initials: LR
authors.lastname: Taggart
authors.forename: Barbara
authors.initials: B
authors.lastname: Mater
authors.forename: Kevin
authors.initials: K
authors.lastname: Katz
authors.forename: Allison
authors.initials: A
authors.lastname: McGeer
mesh_terms: D000328:Adult; D000368:Aged; D002170:Canada; D016022:Case-Control Studies; D015331:Cohort Studies; D004636:Emergency Service, Hospital; D006786:Hospitals, Urban; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000175:diagnosis* / Q000453:epidemiology; D008875:Middle Aged; D058873:Pandemics / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D012307:Risk Factors; D055815:Young Adult