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Outbreak of Gastroenteritis in Wetzel County

This case scenario describes a possible outbreak of gastroenteritis in a nursing home setting. Symptoms include vomiting, diarrhea, and fever with a duration of illness ranging from 10-90 hours. The outbreak is suspected to be caused by Norovirus, a highly contagious virus transmitted through fecal-oral spread.

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Outbreak of Gastroenteritis in Wetzel County

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  1. Outbreak of Gastroenteritis in Wetzel County Thein Shwe, MS, MPH Amber Riba, MPH candidate IDEP/DSDC/OEHP/WVBPH August 6, 2003

  2. Case Scenario Phone call from the local health department reporting a possible outbreak of gastroenteritis in a nursing home setting. • 14 possible cases/ 63 residents • First case: onset of symptoms 2/17 at 11AM • Symptoms include: vomiting, diarrhea, and fever • Duration of illness: 10-90 hours (Mean=30 hours) • No lab testing done

  3. Step 1: Preparation • Prepare for fieldwork • Accumulate knowledge through literature review • Know your role in the investigation

  4. Step 1 • Member of Caliciviridae family • Also known as Norwalk-like virus (NLV) • Named after the original strain “Norwalk virus” • Currently, at least 4 Norovirus genogroups • GI, GII, GIII and GIV – divided into at least 20 genetic clusters

  5. Step 1 • Virus is able to survive • Freezing • Temperatures as high as 60 C • Steamed shellfish • Up to 10 ppm chlorine

  6. Step 1 • The most common cause of acute nonbacterial gastroenteritis in adults • At least 50% of all foodborne outbreaks of GE • Incubation Period: 12-48 hours (median in outbreaks 33 to 36 hours) • Infectious period: 48-72 hours after recovery • Duration of illness: 12-60 hours

  7. Step 1 • Sign and Symptoms: -Nausea -Vomiting (more common in children) -Abdominal Cramps -Diarrhea • Constitutional symptoms: • Headache • Fever (low grade) • Chills • Myalgia • Rarely severe dehydration

  8. Step 1 Mode of Transmission • Fecal-oral spread- primary transmission • Direct person to person • Also airborne and fomite transmission in droplets contaminating surfaces or entering the oral mucosa and being swallowed (no evidence through respiratory system) • Highly contagious • Low infectious dose: <100 viral particles (as few as 10 viral particles)

  9. Step 1 • Outbreaks of Norovirus • Occur in multiple settings • Several mode of transmission • E.g. initial foodborne transmission in a restaurant, followed by secondary person-to-person transmission to household contacts • 232 Norovirus illness outbreaks reported to CDC during July 1997- June 2000

  10. Step 1 • Foodborne Outbreaks of Norovirus Illness • Through direct contamination by a food handler immediately before its consumption • Frequently associated with consumption of cold foods such as various salads, sandwiches, bakery products, salad dressing, cake icing • Contaminated at its source e.g. oysters, raspberries Waterborne outbreaks in community settings caused by sewage contamination of wells and recreational water

  11. Step 3 Verify the Diagnosis • Clinical Presentation plus • Laboratory Confirmation: -Isolation of Norovirus (stool specimen, vomitus, serum) -RT-PCR- sequencing of Norovirus for genotype and cluster identification -Fourfold increase in IgG antibodies in acute and convalescent-phase serum samples -Electron Microscopy

  12. Step 3 continued. Verify the Diagnosis -An illness characterized by all of the following: -Vomiting, the most prominent symptom in >50% of affected persons -Diarrhea -Duration of Illness: 12-60 hours (The Journal of Infectious Diseases. 2000;181(Suppl 2):S281-3 The Impact of Foodborne Calicivirus Disease: The Minnesota Experience)

  13. Step 4 Identify and Count Cases Case: • vomiting OR • 2 or more episodes of diarrhea.

  14. Your Turn

  15. Exercise • Do a Line Listing. • Do Descriptive Epidemiology. • Propose next steps based on your findings.

  16. Line Listing

  17. Step 5 Descriptive Epidemiology • Person • Place • Time

  18. Step 5 Person • N=14 cases -14 cases/ 63 residents (22%) • Age: Range: 68-95 years • Symptom frequencies -Vomiting:14/14 (100%) -Diarrhea: 6/14 (43%) -Fever: 2/14 (14%)

  19. Step 5 Place • Wetzel County • Nursing Home setting

  20. * 19 A-Wing 18 Map of Nursing Home * = Possible Norovirus case * * * * * * * 1 2 * 16 * * 2 * B-Wing 15 * 1 *

  21. Step 5 Time • Symptom onset Range: February 17, 11 AM to February 23rd. • Duration of Illness: 10-48 hrs (except one person – 96 hrs) -Mean: 30 Hours -Median: 24 Hours

  22. What can you tell from this outbreak curve? Person to person ? Point Source ?

  23. What are the next steps? • Develop hypotheses. • Implement Control Measures

  24. Step 6 Develop Hypotheses • Person-to-Person transmission? • Environmental contamination ? • Contaminated food or water? • Aerosolized vomitus?

  25. Step 9 Control Measures Implement Control Measures • Rapid implementation of control measures • Frequent hand washing with soap and water • Thorough and prompt disinfection of the environment • Prevent employee transmission • Use safeguards with laundry • Minimize contact between well and ill • Encourage testing for Norovirus with suspected AGE.

  26. Step 9 • Exclusion of ill foodhandlers for 48 to 72 hours after recovery

  27. Step 10 Communicate Findings to Nursing Home • 14 possible cases out of 63 residents • Symptom onset range: 2/17 to 2/23 • Duration of illness: 10-96 hours • Transmitted through person-to-person • Health Alert to doctors and surrounding LHD

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