Seeing Things: Epidemiology and Outbreak Investigations

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Seeing Things Epidemiology and Outbreak
Investigations

• David Bergmire-Sweat, MPH
• Foodborne Diseases Epidemiologist
• North Carolina Division of Public Health
• August 18, 2009

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Why should we be concerned?

• Foodborne diseases are common 76 million cases
  occur each year in the U.S.
• Foodborne and diarrheal diseases can be
  devastating dehydration, kidney failure,
  mortality among immunocompromised, and fetal death

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Estimated Cases of Selected Foodborne Pathogens

• Agent Food-Related Cases ()

Norwalk-like Viruses 9,200,000
(66.6) Campylobacter 1,963,141 (14.2) Salmo
nella 1,341,873 (9.7) C.
perfringens 248,520 (1.8)
Giardia 200,000 (1.4) S.
aureus 185,060 (1.3)
Shigella 89,648 (0.6) E. coli
O157H7 62,458 (0.5) Rotavirus
39,000 (0.3) Cryptosporidium
30,000 (0.2) Hepatitis A Virus
4,170 (0.0)
Mead, et al 1999
Mead et al, Emerging Infectious Diseases Vol 5,
No. 5 1999
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Most Cases Are Not Reported
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What is an Outbreak?

• Increase in observed cases above what is expected
  in a population in a given area OR group of cases
  that are related to one another because they
  share an exposure
• Four kids with cough and runny nose in a child
  care center in January?
• Woman vomiting after eating at Restaurant X?
• 10 members of the swim team vomiting after eating
  at Restaurant X?
• One case of smallpox?

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Reasons to Investigate Outbreaks

• Identify and eliminate source of infection
• Develop strategies to prevent future outbreaks
• Describe new diseases and learn more about known
  diseases
• Evaluate existing prevention strategies
• Address public concern

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Recent High Profile Outbreaks

• 2006 E. coli O157H7 associated with baby
  spinach 205 cases, 3 deaths, 100 million
• 2006-2007 Salmonella associated with Peter Pan
  Peanut Butter 600 cases, 47 states, recall
  costs alone 60 million
• 2007 Castleberry foods Botulism recall 90
  brands, nationwide recall, 40 million

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Salmonella Saintpaul Associated with Multiple
Vehicles, 2008
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Salmonella Typhimurium 2009 Associated with PCA
Peanut Products
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PulseNet
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Pulsed Field Gel Electrophoresis (PFGE) Patterns
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PulseNet Activity, 1996-2007

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Role of Epidemiology in Outbreak Investigations

• Identify the source, using epidemiologic methods
• Measure difference in exposure between persons
  who became ill and those who did not

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Case-Control Studies

• Compare exposures among ill persons
  (case-patients) and non-ill persons (controls)
• Used when a complete list is not available or too
  large
• Measure of association Odds Ratio

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Interpretation of Odds Ratio

• OR 1.0Same odds of exposure among
  case-patients and controls
• OR gt 1.0Greater odds of exposure among
  case-patients
• OR lt 1.0Lower odds of exposure among
  case-patients

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It Starts with a Phone Call
Union
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Index Cases

• August 26 and August 28, 2007
• Females, White, 13 YO from SC, 15 YO from NC
• Symptoms include nausea, vomiting, diarrhea
  (bloody), abdominal cramps
• Fathers work together in SC, all attended company
  picnic together on August 19, 2007

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Case-patients with and without known turtle
exposure, May 1, 2007 - February 18, 2008 (N107)
No cases reporting turtle exposure
1 case reporting turtle exposure
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Case-patients with and without known turtle
exposure, May 1, 2007 - February 18, 2008 (N107)
No cases reporting turtle exposure
1 case reporting turtle exposure
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Case-Control Study Results
Any lettuce
9/10
17/26
3.5
0.525.0
0.17
Prepackaged lettuce salad
9/10
10/26
8.4
1.259.6
0.01
Brand A prepackaged lettuce salad
9/10
5/23
0.002
10.1
1.567.3
OR odds ratio CI confidence interval
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Brand A Classic Romaine Salad Recovered from
Case-Households
Shared common "Best if Used By Date and
production code
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Product Traceback

• Single processing plant (Soledad, CA)
• Production Date of September 7, 2005
• Lettuce harvested from any 1 of 7 fields

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PFGE Patterns of E. coli O157H7 Isolates from
Lettuce
Source
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Questions to Consider in Assessing PFGE Clusters

• How common is the PFGE subtype?
• How many cases are there?
• Over what time frame did cases occur?
• What is the geographic distribution of cases?
• What are the case demographics?
• Do any of the cases have a red flag exposure?

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Why Epidemiologic Links May Not be Identified for
Cases in a Cluster

• Cases have imperfect recall
• Cases may not know they were exposed
• Secondary transmission
• Cross-contamination
• Traceback failures
• Common pattern confounding issues

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Response for PFGE Clusters

• Minimum Compare case interviews

• Maximum Case-control study

• Food Testing In-between, or in
• conjunction with a case-control study

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PFGE Cluster Investigation - Summary

• A minority of clusters will be identified as
  outbreaks
• This shouldnt be discouraging
• All clusters should be consistently investigated

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Conclusions

• Epidemiology and disease investigation is a
  collaborative discipline
• Local, state and federal partners are all
  involved
• Both an art and a science
• Key skill is to be able recognize meaningful
  patterns in the ongoing data stream

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Acknowledgements
Others
Co-Investigators
Minnesota Department of Agriculture Craig
Braymen Minnesota Department of Health Selina
Jawahir and Kirk Smith Centers for Disease
Control and Prevention Chris Braden and Molly
Joyner
California Department of Health Services Food and
Drug Branch Jeff Farrar and Benson Yee Oregon
Public Health Services William Keene Minnesota
Department of Agriculture Kevin Elfering and
Heidi Kassenborg Minnesota Department of
Health David Determan, Ellen Laine, Brian Lee and
Carlota Medus Wisconsin Department of
Health John Archer U.S. Food and Drug
Administration
Disclaimer The findings and conclusions in this
presentation are those of the author(s) and do
not necessarily represent the views of the
Centers for Disease Control and Prevention.