Identification, management, and clinical characteristics of hospitalized patients with influenza-like illness during the 2009 H1N1 influenza pandemic, Cook County, Illinois

Infect Control Hosp Epidemiol. 2011 Oct;32(10):998-1002. doi: 10.1086/661912. Epub 2011 Aug 30.


Objective: To describe the identification, management, and clinical characteristics of hospitalized patients with influenza-like illness (ILI) during the peak period of activity of the 2009 pandemic strain of influenza A virus subtype H1N1 (2009 H1N1).

Design: Retrospective review of electronic medical records.

Patients and setting: Hospitalized patients who presented to the emergency department during the period October 18 through November 14, 2009, at 4 hospitals in Cook County, Illinois, with the capacity to perform real-time reverse-transcriptase polymerase chain reaction testing for influenza.

Methods: Vital signs and notes recorded within 1 calendar day after emergency department arrival were reviewed for signs and symptoms consistent with ILI. Cases of ILI were classified as recognized by healthcare providers if an influenza test was performed or if influenza was mentioned as a possible diagnosis in the physician notes. Logistic regression was used to determine the patient attributes and symptoms that were associated with ILI recognition and with influenza infection.

Results: We identified 460 ILI case patients, of whom 412 (90%) had ILI recognized by healthcare providers, 389 (85%) were placed under airborne or droplet isolation precautions, and 243 (53%) were treated with antiviral medication. Of 401 ILI case patients tested for influenza, 91 (23%) had a positive result. Fourteen (3%) ILI case patients and none of the case patients who tested positive for influenza had sore throat in the absence of cough.

Conclusions: Healthcare providers identified a high proportion of hospitalized ILI case patients. Further improvements in disease detection can be made through the use of advanced electronic health records and efficient diagnostic tests. Future studies should evaluate the inclusion of sore throat in the ILI case definition.

Publication types

  • Multicenter Study
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Academic Medical Centers
  • Adolescent
  • Adult
  • Age Distribution
  • Aged
  • Antiviral Agents / therapeutic use
  • Child
  • Child, Preschool
  • Electronic Health Records
  • Emergency Service, Hospital
  • Female
  • Humans
  • Illinois / epidemiology
  • Infant
  • Infant, Newborn
  • Influenza A Virus, H1N1 Subtype / isolation & purification*
  • Influenza, Human / diagnosis*
  • Influenza, Human / drug therapy
  • Influenza, Human / epidemiology*
  • Logistic Models
  • Male
  • Middle Aged
  • Pandemics
  • Real-Time Polymerase Chain Reaction
  • Retrospective Studies
  • Young Adult


  • Antiviral Agents