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Evaluating a Syndromic Surveillance System for the Detection of Acute Infectious Gastroenteritis Outbreaks ---North Carolina, 2004

Emily E. Sickbert-Bennett,1 M. Scholer,2 J. Butler,3 D. Travers,2 J. MacFarquhar,4 A. Waller,2 G. Ghneim5
1
University of North Carolina Healthcare System, Chapel Hill, North Carolina; 2University of North Carolina at Chapel Hill, Department of Emergency Medicine, Chapel Hill, North Carolina; 3Orange County Health Department, Hillsborough, North Carolina; 4North Carolina Statewide Program for Infection Control and Epidemiology, Chapel Hill, North Carolina; 5North Carolina General Communicable Disease Control Branch, Division of Public Health, Raleigh, North Carolina

Corresponding author: Emily E. Sickbert-Bennett, UNC Health Care System, Hospital Epidemiology, 1001 West Wing CB #7600, 101 Manning Drive, Chapel Hill, NC 27514. Telephone: 919-843-4165; Fax: 919-966-1451; E-mail: esickber@unch.unc.edu.

Disclosure of relationship: The contributors of this report have disclosed that they have no financial interest, relationship, affiliation, or other association with any organization that might represent a conflict of interest. In addition, this report does not contain any discussion of unlabeled use of commercial products or products for investigational use.

Abstract

Introduction: During January 21--February 9, 2004, a norovirus outbreak occurred among University of North Carolina (UNC) students, some of whom sought care at the UNC hospital's emergency department (ED). Despite an established ED-based syndromic surveillance system using CDC's Early Aberration Reporting System (EARS), no increases in gastrointestinal illness (GI) were detected during the outbreak period.

Objectives: This study used outbreak data to evaluate North Carolina's syndromic surveillance system and GI case definition.

Methods: The hospital ED electronically sent data for all visits to a state data repository. Recorded chief complaints, vital signs, and triage nurse notes were searched electronically for key terms to assign ED visits to CDC syndrome classifications. The GI case definition criteria required at least one constitutional symptom and one GI symptom. The outbreak line-listing of 429 cases as determined by the local health department was reviewed, patient age distribution examined, and hospital records used to identify ED patients by name. Data on these case-patients were reviewed and each symptom recorded. On the basis of the symptom frequency, a modified GI case definition was drafted and tested on the ED data from the time of the outbreak. The data were stratified by the age distribution of the known outbreak cases. The number of GI cases that met the modified definition was examined for aberrations by using EARS.

Results: Of the 11 case-patients seen in the ED, one was identified with syndromic surveillance by using the original GI case definition. Of the 42 remaining ED visits during the outbreak period that were classified as GI syndrome, eight (19%) were misclassified as a result of lack of recognition of negation terms (e.g., no fever), and 34 (81%) were classified correctly. Frequency analysis of the 11 known ED case-patients' symptoms indicated nausea and vomiting, 11 (100%); diarrhea, nine (82%); abdominal pain, eight (73%); fever, two (18%); and body aches, one (9%). When a modified GI case definition that did not require a constitutional symptom (e.g., fever) was used and syndromic cases were stratified by age distribution for persons aged 17--22 years, all 11 cases were captured, and an aberration was detected on January 21, the first day of the outbreak.

Conclusion: Automated systems must be monitored to ensure proper syndrome classification. For syndromic surveillance to be used to detect both biologic terrorism--related and community outbreaks, case definitions must be constructed with careful consideration of different clinical presentations with different etiologies and illness severities.

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Date last reviewed: 8/5/2005

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