Seeing Things: Epidemiology and Outbreak Investigations

1. Seeing Things: Epidemiology and Outbreak Investigations David Bergmire-Sweat, MPH Foodborne Diseases Epidemiologist North Carolina Division of Public Health August 18, 2009

2. 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

3. Estimated Cases of Selected Foodborne Pathogens Agent Food-Related Cases (%) Norwalk-like Viruses 9,200,000(66.6) Campylobacter 1,963,141 (14.2) Salmonella 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 O157:H7 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

4. Most Cases Are Not Reported

5. 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?

6. 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

7. Recent High Profile Outbreaks • 2006 – E. coli O157:H7 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

8. Salmonella Saintpaul Associated with Multiple Vehicles, 2008

9. Salmonella Typhimurium 2009 Associated with PCA Peanut Products

10. PulseNet

11. Pulsed Field Gel Electrophoresis (PFGE) Patterns

12. PulseNet Activity, 1996-2007

14. 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

15. 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

16. Interpretation of Odds Ratio • OR = 1.0Same odds of exposure among case-patients and controls • OR > 1.0Greater odds of exposure among case-patients • OR < 1.0Lower odds of exposure among case-patients

17. It Starts with a Phone Call Union

18. 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

19. Case-patients with and without known turtle exposure,May 1, 2007 - February 18, 2008 (N=107) No cases reporting turtle exposure ≥1 case reporting turtle exposure

20. Case-patients with and without known turtle exposure,May 1, 2007 - February 18, 2008 (N=107) No cases reporting turtle exposure ≥1 case reporting turtle exposure

21. Exposure Cases Controls Matched OR* 95% CI† p-value Case-Control Study Results Any lettuce 9/10 17/26 3.5 0.5–25.0 0.17 Prepackaged lettuce salad 9/10 10/26 8.4 1.2–59.6 0.01 Brand A prepackaged lettuce salad 9/10 5/23 10.1 1.5–67.3 0.002 * OR = odds ratio† CI = confidence interval

22. Brand A Classic Romaine Salad Recovered from Case-Households Shared common "Best if Used By” Date and production code

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

24. Initial Minnesota Case-patient Classic RomaineBag #1 Classic Romaine Bag #2 PFGE Patterns of E. coli O157:H7 Isolates from Lettuce Source

25. 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?

26. 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

27. Response for PFGE Clusters • Minimum: Compare case interviews • Maximum: Case-control study • Food Testing: In-between, or in • conjunction with a case-control study

28. PFGE Cluster Investigation - Summary • A minority of clusters will be identified as outbreaks • This shouldn’t be discouraging • All clusters should be consistently investigated

29. 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

30. 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.