Detecting and Investigating Foodborne Outbreaks

1. Detecting and Investigating Foodborne Outbreaks Ian Williams PhD, MS Chief, Outbreak Response and Prevention Branch Centers for Disease Control and Prevention, USA Dubai, February 2014

2. Objectives At the end of this lecture, youwillbe able to: • Describe how outbreaks are detected • Explain the steps in investigating an outbreak • Identify the necessarycollaborators for an outbreak investigation, includingepidemiologists, laboratorians, environmentalhealthspecialists, amongothers

3. Last meal bias: A common problem • When people develop an enteric (diarrheal) illness that might be caused by food, most people think the last meal they ate is what made them sick • This is not true in most instances, especially for bacterial pathogens (like salmonella) • In a outbreak that is suspected to be related to food, it is important to understand and follow certain steps in the investigation • Requires collaboration between laboratorians, epidemiologists, and environmental health specialists

4. Successful outbreak investigation depends on collaboration

5. Successful outbreak investigation depends on collaboration Experts on surveillance and investigating illness in humans Experts on testing samples from humans and food Experts on food preparation and food production

6. What is an outbreak? The occurrence of cases of an illness clearly in excess of the normal expectancy Where you work, how are outbreaks detected?

7. Laboratory confirmed cases are the tip of the iceberg Lab-confirmed case reported

8. Outbreak detection and interventions can occur at all levels Pyramid (iceberg) of laboratory-based surveillance Laboratory- based surveillance Laboratory- based surveillance Lab-confirmed case reported Lab identifies pathogen Sample submitted to lab Syndromic surveillance Doctor requests sample Person goes to doctor Public complaints Person has symptoms

9. Causes of an increased number of cases Artificial increase Change in lab methods Change in reporting Data entry errors Real increase Increased population size Change in population characteristics Random variation Outbreak Is it an outbreak?

10. Why investigate foodborne outbreaks? • Immediate goal: prevent more illnesses from this outbreak • Longer-term goals • identify pathogens that often cause outbreaks • identify food vehicles that often cause outbreaks • Identify common settings and contributing factors • identify gaps in the food safety system to take action to prevent future outbreaks and illnesses

11. Steps in investigatingan outbreak • Detect the outbreak and assemble a team • Gather descriptive information • Generate hypotheses • Test hypotheses • Determine how and where contamination occurred • Prevent more illnesses • Communicate

13. Step 1. Detect the outbreak and assemble a team • Ways outbreaks are detected • informal reports, e.g., physician, ill persons, clinical laboratory • notifiable disease surveillance • laboratory-based surveillance subtyping results, e.g., • Salmonella serotyping • antibiotic resistance pattern • pulsed-field gel electrophoresis (PFGE) • phage typing Step 1: Detect the outbreak and assemble a team

14. Types of foodborne outbreaks Traditional Scenario New Scenario Seemingly unlinked cases Widely distributed foods Foods with long shelf-life, or ready-to-eat, or that require no or little consumer handling • Cases clustered in time and space • Common meal or event • Result of food handling error Step 1: Detect the outbreak and assemble a team

15. Traditional scenario “point source” foodborne outbreak

16. New scenario “ongoing exposure” foodborne outbreak E. coli O157 outbreak Step 6: Prevent more Illnesses

17. Example: United States, 2009 • On May 19, PulseNet identified 17 human Escherichia coli O157 isolates with a particular pulsed-field gel electrophoresis (PFGE) pattern uploaded in May • On average, 6 to 7 isolates with this pattern uploaded each month Step 1: Detect the outbreak and assemble a team

18. Shiga toxin-producing E. coli O157 • Causes diarrhea, often bloody • can be severe in children and elderly • hemolytic uremic syndrome (HUS) is a complication • causes kidney failure • Usual food vehicles: ground beef, leafy greens, unpasteurized milk Step 1: Detect the outbreak and assemble a team

19. Assemble a team • Contact key groups • local, regional, national • laboratory, epidemiology, health inspectors, food regulators, communicators, clinicians, others • Determine responsibilities • collect and analyze data • implement control measures • communicate Step 1: Detect the outbreak and assemble a team

20. Successful outbreak investigation depends on collaboration

21. Steps in investigatingan outbreak • Detect the outbreak and assemble a team • Gather descriptive information • Generate hypotheses • Test hypotheses • Determine how and where contamination occurred • Prevent more illnesses • Communicate

22. Step 2: Gather descriptive information 2a: Determine the etiology 2b: Describe the outbreak by time, place, and person 2c: Write a case definition 2d: Look for more cases The order of these steps can vary depending on the investigation

23. 2a: Determine the etiology • If the outbreak was detected by public complaint or syndromic surveillance, determine the etiology • use symptoms, incubation period, etc, to determine possible etiologies • decide which lab tests are needed (eg, bacterial stool culture) • collect specimens from ill persons and test them Step 2: Gather descriptive information. Step 2a: Determine the etiology

24. Food testing does not determine the etiology • Collect food samples for laboratory testing • IF preliminary data points to certain foods • epidemiologists, food regulatory authorities, and laboratorians discuss and then decide appropriate tests on food • be aware of limitations of food testing Do not expect to learn the etiology from laboratory testing of food! Do not delay investigation awaiting tests on food! Talk to lab! Step 2: Gather descriptive information. Step 2a: Determine the etiology

25. False negative tests of food Why might the lab not identify the etiologic agent in a food that caused the outbreak? Step 2: Gather descriptive information. Step 2a: Determine the etiology

26. Why the laboratory may not find the etiologic agent in food • Collection reasons • sample was improperly collected or transported • the actual food that caused illness was not sampled • Food reasons • all the food that caused illness was consumed • only some parts of the food were contaminated • the etiologic agent did not survive in the food • Lab reasons • the laboratory does not test for the agent • the lab test is not sensitive enough to detect the agent • there is no lab test for the agent Talk to lab! Step 2: Gather descriptive information. Step 2a: Determine the etiology

27. False positive tests of food Why might lab identify a pathogen in a food that did not cause the outbreak? Step 2: Gather descriptive information. Step 2a: Determine the etiology

28. False positive tests on food The lab may identify a pathogen that did not cause the outbreak • Food reasons • foods may be contaminated with pathogens unrelated to the outbreak • especially true for raw meat and poultry • Lab reasons: false positive results, errors In most diarrheal outbreaks, you will learn more by collecting specimens from ill people than from food Step 2: Gather descriptive information. Step 2a: Determine the etiology

29. Step 2: Gather descriptive information 2a: Determine the etiology 2b: Describe the outbreak by time, place, and person 2c: Write a case definition 2d: Look for more cases

30. When did the illnesses occur? Where did illnesses occur? Who was affected? age, sex symptoms and signs number ill, hospitalized, died Step 2b: Describe outbreak by time, place, person Step 2: Gather descriptive information. Step 2b: Describe by time, place, person

31. Step 2b: Describe outbreak by time, place, person • When did the illnesses occur? • Where did illnesses occur? • Who was affected? • age, sex • what were the symptoms and signs? • % hospitalized • % died Draw an epidemic curve Make a map Summarize in a table Step 2: Gather descriptive information. Step 2b: Describe by time, place, person

32. Epi curve made at start of investigation Step 2: Gather descriptive information. Step 2b: Describe by time, place, person

33. Map made at start of investigation Step 2: Gather descriptive information. Step 2b: Describe by time, place, person

34. Table of patient characteristics Median age (range): 15 years (2 – 65 years) Step 2: Gather descriptive information. Step 2b: Describe by time, place, person

35. Step 2: Gather descriptive information 2a: Determine the etiology 2b: Describe the outbreak by time, place, and person 2c: Write a case definition 2d: Look for more cases

36. 2c: Write a case definition • Components: illness, pathogen, time, place • Case types: possible, probable, confirmed Include the lab in the discussion Step 2: Gather descriptive information. Step 2c: Write a case definition

37. Talk to lab! E. coli O157 infection, and PFGE pattern indistinguishable from outbreak strain, and multi-locus variable-number tandem repeat analysis (MLVA) pattern indistinguishable from outbreak strain pattern and illness began (or isolation date if date illness began is not available) on or after March 1, 2009 Example: Confirmed case definition, US outbreak of E. coli O157 infections Some outbreaks also have definitions for probable and possible cases Step 2: Gather descriptive information. Step 2c: Write a case definition

38. DNA sequence-based subtyping technique During outbreak investigations PFGE alone might not differentiate between outbreak-associated and unrelated cases adding MLVA information can help What is MLVA? Step 2: Gather descriptive information. Step 2c: Write a case definition

39. Step 2: Gather descriptive information 2a: Determine the etiology 2b: Describe the outbreak by time, place, and person 2c: Write a case definition 2d: Look for more cases

40. 2d: Look for more cases • Purpose of case finding • treat ill persons • prevent secondary cases • determine location and magnitude of outbreak • find clues about source Why does finding more cases increase the likelihood of a successful investigation? What can you do to find more cases? Step 2: Gather descriptive information. Step 2d: Look for more cases

41. 2d: Ways to look for more cases • Request information from health care providers • Review calls to health department from ill persons • Request information from clinical laboratories • Review notifiable disease reports to health department • Contact nearby health departments to see if they have similar illnesses • Assure strong communication between epidemiology and laboratory groups • In special circumstances, request information directly from the public, via the media Step 2: Gather descriptive information. Step 2d: Look for more cases

42. Steps in investigatingan outbreak • Detect the outbreak and assemble a team • Gather descriptive information • Generate hypotheses • Test hypotheses • Determine how and where contamination occurred • Prevent more illnesses • Communicate

43. 3: Generate hypotheses • Promptly, thoroughly interview some cases to • identify common exposures • eliminate uncommon exposures • Alternative interview methods • one investigator conducts open-ended interviews with 5-10 ill persons, or • one or more investigators conduct interviews with some ill persons using a detailed “hypothesis-generating” questionnaire

44. Example: US outbreak of E. coli O157 infections First, used “hypothesis-generating” questionnaire to interview cases • several epidemiologists did interviews • Findings (no strong hypothesis emerged): • Possible vehicles • ground beef • strawberries • ice cream • Unlikely vehicles • spinach • unpasteurized dairy • animal contact Step 3: Generate hypotheses

45. Example: US outbreak of E. coli O157 Infections Then, they tried a different approach • One investigator interviewed 5 people with recent illness from one state (Washington) • open-ended, conversational interviews conducted during June 13 - 16 • asked about exposures during week before illness Step 3: Generate hypotheses

46. Open-ended interview results What patients reported: • 5 of 5 ate ground beef • 3 of 5 ate strawberries • 5 of 5 ate raw cookie dough • 4 of 5 ate Brand X raw cookie dough On June 16, presented these data to investigation group • Maryland, Iowa, Illinois, and Minnesota reported that patients they interviewed also ate raw cookie dough! Raw cookie dough documented in notes from first interview Step 3: Generate hypotheses

47. Finally, a hypothesis! Raw cookie dough as a vehicle? • some questioned biological plausibility • never before linked to E. coli outbreak Based on epidemiologic evidence, raw cookie dough became a leading hypothesis Step 3: Generate hypotheses

48. Steps in investigatingan outbreak • Detect the outbreak and assemble a team • Gather descriptive information • Generate hypotheses • Test hypotheses • Determine how and where contamination occurred • Prevent more illnesses • Communicate

49. Step 4: Test hypotheses Do a study only after you have a strong hypothesis! • 4a: Gather data relevant to the hypothesis • 4b: Design a study • 4c: Analyze the study

50. Step 4a. Gather data relevant to the hypothesis • Discuss possible steps with food safety agencies • For point source outbreaks, restaurant inspection history, etc. • For dispersed outbreaks, product distribution • what regions of country, which stores • could the product come from one factory? • Consider collecting data from patients • information on food packages • leftover food Step 4: Test hypothesis. Step 4a: Gather data relevant to hypothesis