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Anatomy of an Outbreak

Anatomy of an Outbreak. Kirk Smith, DVM, MS, PhD Supervisor, Foodborne, Vectorborne, and Zoonotic Diseases Unit Acute Disease Investigation and Control Section Minnesota Department of Health. kirk.smith@state.mn.us Office phone: 651-201-5240.

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Anatomy of an Outbreak

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  1. Anatomy of an Outbreak Kirk Smith, DVM, MS, PhD Supervisor, Foodborne, Vectorborne, and Zoonotic Diseases Unit Acute Disease Investigation and Control Section Minnesota Department of Health kirk.smith@state.mn.us Office phone: 651-201-5240

  2. Some Recent Notable Multi-state Foodborne Outbreaks of Salmonellosis • Peter Pan peanut butter • 714 cases • 48 states • PCA peanut butter • 691 cases • 46 states • Cake Mix • 25 cases • 9 states • Hot peppers • 1,442 cases • 44 states • Tomatoes • 183 cases • 21 states • Veggie Booty • 70 cases • 23 states • Pot pies • 401 cases • 42 states 2005 2006 2007 2008

  3. Diseases Reportable to the Minnesota Department of Health FOODBORNE AND WATERBORNE DISEASES * Submit isolates or clinical materials to the Minnesota Department of Health Botulism (Clostridium botulinum) Campylobacteriosis (Campylobacter sp.)* Cholera (Vibrio cholerae)* Cryptosporidiosis (Cryptosporidium sp.) Enteric Escherichia coli infection (E. coli O157:H7 and other pathogenic E. coli from gastrointestinal infections)* Giardiasis (Giardia lamblia) Hemolytic uremic syndrome Listeriosis (Listeria monocytogenes)* Salmonellosis, including typhoid (Salmonella sp.)* Shigellosis (Shigella sp.)* Toxoplasmosis Yersiniosis (Yersinia sp.)*

  4. 1 - 7 days (incubation) 2 - 4 days Person eats contaminated food Goes to doctor, stool sample collected Becomes ill 2 - 3 days Confirmation/ serotyping, PFGE subtyping Submission of isolate to public health lab 2 - 5 days 1 - 5 days Stool sample positive Interview Report of case to public health Lab and epi data combined

  5. Reportable Bacterial Enteric Pathogen Surveillance in Minnesota • Isolates must be submitted to the Minnesota Department of Health • Real-time pulsed-field gel electrophoresis (PFGE) subtyping of all isolates • Routine, real-time interviews of all cases

  6. Pulsed-Field Gel Electrophoresis (PFGE) 1.5 hours DNA Bacteria Molten agarose Lysis Enzyme digestion (XbaI) Pulse electrophoresis 1.5 hours 18 hours

  7. The National Molecular Subtyping Network for Foodborne Disease Surveillance Area Labs National Database FoodNet Sites FDA, USDA Lab

  8. PulseNet Laboratory Network PulseNet National Databases (CDC) Participating Labs PFGE Patterns Local Databases

  9. Bacterial Isolate Flow from Clinical Labs to Public Health Labs • Completeness and timeliness of isolate submission to public health labs, and timeliness of serotyping/PFGE subtyping at public health labs, determines the sensitivity of outbreak detection • i.e., need this for optimal detection of outbreaks (local and multistate) caused by Salmonella, E. coli O157:H7

  10. Minnesota Surveillance Philosophy • Interview all cases, ASAP • Collect details on specific exposures • Restaurant, grocery store names • Brand names • Open-ended food histories • Investigation of all PFGE clusters • Intensity/resource expenditure depends on the exact nature of the cluster • Follow leads aggressively

  11. Standard Questionnaire for Salmonella, E. coli O157 cases

  12. Minnesota Surveillance Philosophy • Interview all cases, ASAP • Collect details on specific exposures • Restaurant, grocery store names • Brand names • Open-ended food histories • Investigation of all PFGE clusters • Intensity/resource expenditure depends on the exact nature of the cluster • Follow leads aggressively

  13. Response for PFGE Clusters • Minimum: Compare case interviews • Maximum: Case-control study • Food Testing: Before, during, or after case control study • “Informational” product tracing

  14. Minnesota Approach to Investigation of PFGE Clusters: Dynamic Cluster Investigation Model Case #1 Case #2 Case #3 Case #4

  15. Initial trawling questionnaire interview date 9/10 9/27 10/4 afternoon 2 PP Exposure added 1 3 4 Consumed Banquet PP “trawling” questionaire Dynamic Cluster Investigation - Pot Pies 10/3 night 10/4 evening 10/4 morning Re-interviewed cases about frozen foods and pot pies

  16. Team Diarrhea Fall 2007

  17. Epidemiologic Follow-up of Cases • Determines the likelihood of identifying the source of an outbreak

  18. Epidemiologic Data are Dirty • Not all exposed people get sick • Some people get sick without being exposed • Not all “exposed people” are really exposed • Not all “unexposed people” are really unexposed • Not all sick people are really sick

  19. Presentations of Outbreaks due to Commercially Distributed Food Items • Cases in community, no obvious common exposure • Retail food (grocery stores) • Cases occur among patrons of restaurant(s) • Cases clustered in institution(s) • Any combination of above three

  20. Presentations of Outbreaks due to Commercially Distributed Food Items • Cases in community, no obvious common exposure • Retail food (grocery stores) • Cases occur among patrons of restaurant(s) • Cases clustered in institution(s) • Any combination of above three

  21. Dole Prepackaged Salad O157 Outbreak September 27, 2005 • Three O157 isolates with indistinguishable PFGE patterns identified by Minnesota Public Health Laboratory • PFGE pattern new in Minnesota, rare in United States • 0.35% of patterns in National Database

  22. Outbreak Investigation - Methods September 28–29, 2005 • Additional O157 isolates received and subtyped by PFGE • 7 isolates demonstrated outbreak PFGE subtype • Supplemental interview form created • Case-control study initiated • Age-matched community controls recruited through sequential digit dialing anchored on case’s telephone number

  23. Case-Control Study Results Cases Exposure Controls Matched OR* 95% CI† p-value 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

  24. E. coli O157:H7 Cases Associated with Brand A Prepackaged Lettuce by Date of lllness Onset 7 6 5 Case-control study implicated Brand A salad. Number of Cases 4 Case-control study initiated. 3 Initial cluster of 3 isolates among MN residents identified. 2 1 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 September October Date of Onset2005

  25. E. coli O157:H7 Cases Associated with Brand A Prepackaged Lettuce by Date of lllness Onset 7 6 5 Case-control study implicated Brand A salad. Number of Cases 4 Case-control study initiated. 3 Initial cluster of 3 isolates among MN residents identified. 2 1 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 September October Date of Onset2005

  26. Minnesota Additional states E. coli O157:H7 Cases Associated with Brand A Prepackaged Lettuce (n=26) 7 6 OR 5 Number of Cases 4 3 WI 2 WI 1 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 1 2 3 4 September October Date of Onset2005

  27. Presentations of Outbreaks due to Commercially Distributed Food Items • Cases in community, no obvious common exposure • Retail food (grocery stores) • Cases occur among patrons of restaurant(s) • Cases clustered in institution(s) • Any combination of above three

  28. Two cases name Restaurant A Salmonella Saintpaul Patron Cases Associated with Restaurant A by Date of Isolate Receipt in MDH Laboratory, June 2008 7 6 5 Number of Cases 4 3 2 1 22 23 24 25 26 27 28 29 30 1 2 3 4 June Date of Isolate Receipt

  29. Restaurant A Outbreak June 30, 2008 • MDH and Ramsey County staff visited restaurant • Interviewed management and employees • Collected invoices for ingredients used in dishes consumed by cases • Requested credit card receipts from same time period • Obtained copies of menu

  30. Second case names Restaurant A Visit restaurant Initial case-control study/traceback results to CDC Salmonella Saintpaul Patron Cases Associated with Restaurant A by Date of Isolate Receipt in MDH Laboratory, June 2008 7 6 5 Number of Cases 4 3 2 1 22 23 24 25 26 27 28 29 30 1 2 3 4 June Date of Isolate Receipt

  31. Univariate and Multivariate Results of Minnesota Case-Control study

  32. Presentations of Outbreaks due to Commercially Distributed Food Items • Cases in community, no obvious common exposure • Retail food (grocery stores) • Cases occur among patrons of restaurant(s) • Cases clustered in institution(s) • Any combination of above three

  33. December 3, 2008

  34. 1st 11 cases in MN Institutional link, Implication of PB

  35. S. Typhimurium Investigation, 2008-2009 November 17-24, 2008 MDH received 3 outbreak isolates Early December Leading hypothesis in national investigation was chicken Restaurant-associated outbreak in another state with three PFGE patterns Ultimately shown to be a “red herring”

  36. Minnesota S. Typhimurium Investigation December 10-19, 2008 MDH received 8 additional outbreak isolates All chicken for first 4 cases traced back - source did not converge with other state’s investigation or with each other First 8 interviewed cases reported eating peanut butter Suspicious, but not enough evidence to implicate one product, or even peanut butter overall, as the vehicle

  37. Minnesota S. Typhimurium Investigation December 22, 2008 • Medical director of LTCF (LTCF A) in northern MN reports confirmed Salmonella infections in 3 residents • Specimens from 2 other residents pending • All five cases confirmed with outbreak strain of S. Typhimurium • Outbreak cases identified in other institutions

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