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600 Identification, Management and Clinical Characteristics of Hospitalized Patients with Influenza-like Illness (ILI) during the 2009 H1N1 Pandemic, Cook County, IL

Sunday, April 3, 2011
Trinity Ballroom (Hilton Anatole)
Kristen E. Metzger, MPH , Chicago Department of Public Health, Chicago, IL
Stephanie R. Black, MD, MSc , Chicago Department of Public Health, Chicago, IL
Roderick C. Jones, MPH , Chicago Department of Public Health, Chicago, IL
Shaun R. Nelson, MPH , Cook County Department of Public Health, Oak Park, IL
Ari Robicsek, MD , NorthShore University HealthSystem, Evanston, IL
Gordon M. Trenholme, MD , Rush University Medical Center, Chicago, IL
Mary Alice Lavin, RN, MJ , Rush University Medical Center, Chicago, IL
Stephen G. Weber, MD, MSc , University of Chicago Medical Center, Chicago, IL
Sylvia Garcia-Houchins, RN , University of Chicago Medical Center, Chicago, IL
Emily Mawdsley, MD , University of Chicago Medical Center, Chicago, IL
Jorge P. Parada, MD, MPH , Loyola University Medical Center, Maywood, IL
Susan I. Gerber, MD , Cook County Department of Public Health, Oak Park, IL

Background: With the emergence of 2009 H1N1, the rapid identification of potential influenza infections among hospitalized patients was necessary in order to insure optimal patient management and infection control, and meet new public health reporting guidelines.  ILI is a simple symptom complex commonly used to identify potential influenza cases.

Objective: To describe the identification, management and clinical characteristics of ILI cases hospitalized during the height of 2009 H1N1 pandemic in the Chicago area.

Methods: We conducted a retrospective electronic medical records review of patients admitted to 4 Cook County hospitals who presented to the emergency department October 18-November 14, 2009.  Vital signs flowsheets and nurse and physician notes recorded within 1 calendar day of ED arrival were reviewed for signs and symptoms consistent with our ILI case definition (temperature ≥100°F, or subjective fever, with cough and/or sore throat, in the absence of a known cause other than influenza).  ILI cases were classified as recognized by healthcare providers (HCPs) if a PCR test for influenza was performed, or influenza was mentioned as a possible diagnosis in the physician notes.  Logistic regression was used to determine patient attributes and symptoms associated with ILI recognition and influenza infection.   

Results: The figure summarizes the numbers of cases assessed, recognized as ILI, tested for influenza and reported to public health authorities.  We identified 460 ILI cases, of which 412 (90%) were recognized by HCPs, 389 (85%) were placed in airborne or droplet isolation and 243 (53%) were treated with antiviral medication.  Patients with ILI had fever and the following symptoms: cough and sore throat, 133 (29%); cough in the absence of sore throat, 313 (68%); sore throat in the absence of cough, 14 (3%).  None of the ILI cases that tested positive for influenza had sore throat in the absence of cough.  After adjusting for patient age and hospital, myalgias (OR 4.5, 95% CI 1.7-11.7, p=.002), chills (OR 3.1, 95% CI 1.4-6.6, p=.004) and asthma (OR 5.2, 95% CI 1.5-17.8, p=.008) were significantly associated with ILI recognition; shortness of breath (OR 2.4, 95% CI 1.3-4.4, p=.005) and increasing temperature, in degrees over 100°F (OR 1.4, 95% CI 1.1-1.6, p=.002) were significantly associated with testing positive for influenza. 

Conclusions: During peak 2009 H1N1 activity, HCPs identified 90% of hospitalized ILI cases.  Sore throat without cough was rare among ILI cases, and absent among cases that tested positive for influenza.  ILI cases with myalgias, chills and asthma were more likely to be recognized by HCPs.  ILI cases with elevated temperature and shortness of breath were more likely to test positive for influenza.