Foodborne illness attorney Bill Marler speaks to a Hyla Middle School Science about how food poisoning outbreaks are investigated

1. Hyla Middle
School Science
Making the Causal
Link: Investigating
Foodborne Disease
Outbreaks
William D. Marler, Esq.

2. CDC Estimates of Foodborne Illness
• 48 million cases of
foodborne illness annually
• 125,000 hospitalizations
• 3,000 deaths

3. Estimates Differ From Actual Counts
• Annual E. coli O157
estimates
– 62,000 illnesses
– 1,800 hospitalizations
– 52 deaths
• But, only 2,621 E. coli
0157 cases were
reported in 2005

4. Notifiable/Reportable Diseases
• Reporting authorized by Congress in 1878
• Nationally Reportable Diseases
- 1993 (food or water borne origin)
Botulism, Cryptosporidiosis, Cyclosporiasis, Giardiasis, Hemolytic
Uremic Syndrome (post-diarrheal), Hepatitis A, Listeriosis,
Salmonellosis, Shiga toxin producing Escherichia coli (STEC),
Shigellosis, Trichinosis, Vibriosis
http://www.cdc.gov/ncphi/disss/nndss/phs/infdis2008.htm

5. Pathway of a Foodborne Illness
Investigation

6. Pathway of a Foodborne Illness
Investigation
If there are more ill
persons than expected,
an OUTBREAK might be
underway.

7. How Do We Know If There Is an Excess?
Public Health Surveillance
The ongoing collection, analysis,
interpretation and dissemination of health
data directed towards the control and
prevention of diseases.

8. Pathway of a Foodborne Illness
Investigation

9. Typical Steps of an Outbreak
Investigation
• Verify the diagnosis
• Establish that an outbreak is occurring
• Define and identify cases
• Orient the data in terms of person, place,
and time
• Develop and test the hypotheses
• Case Control Study
• Refine the hypotheses and carry out additional
studies
• Implement control and prevention measures
• Report findings

10. A Word to the Wise!
• No mandatory list
of how to proceed
• No set order of steps
to take
• Investigation is dynamic:
case definition, line
listings, descriptive
epidemiology,
hypotheses can change
• Expect the unexpected

11. Investigative Partners
• Laboratory investigators
– Microbiologic diagnosis
– Virology/Parasitic Labs
– Molecular analysis
• Epidemiologic investigators
– Individual case interviews
– Outbreak investigation
• Cohort studies
• Case/control studies
• Environmental investigators
– Facility investigation
– Environmental sampling
– Product traceback

12. Epidemiology–Basic Tools of the Trade
Real-time interviewing with a broad-based
exposure questionnaire
• Symptoms
• Incubation
• Duration
• Food History
• Medical Attention
• Suspected source
• Others Ill

13. Pulsed Field Gel Electrophoresis (PFGE)
A Powerful Outbreak Detection Tool
• Process separates
chromosomal fragments of
intact bacterial genomic DNA
grown from patient isolate
• Results in 10 to 20 DNA
fragments which distinguish
bacterial strains
• Genetic relatedness among
strains is based on similarities
of the DNA patterns
• Outbreak strains are those
that are epidemiologically
linked AND genetically linked

14. 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?

15. E. coli O157:H7 Outbreak,
Minnesota, September 2005
Thanks to MN DOH “Team D” for use of the following slides!
Team Diarrhea

16. Outbreak Detection
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
• Patients reported eating prepackaged salad;
no other potential common exposures evident

17. E. coli O157:H7 Cases Associated
with Dole Prepackaged Lettuce
7
Number of Cases
6
5
4
3
2 Initial cluster of 3 isolates
among MN residents
1 identified.
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 Onset 2005

18. Outbreak Investigation - Methods
September 28–29, 2005
• Additional O157 isolates received
at the MDOH and subtyped by PFGE
– 7 isolates demonstrated outbreak PFGE
subtype
• Supplemental interview form created
• Case-control study initiated

20. E. coli O157:H7 Cases Associated
with Dole Prepackaged Lettuce
7
Number of Cases
6
5
4
Case-control study initiated.
3
2 Initial cluster of 3 isolates
among MN residents
1 identified.
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 Onset 2005

21. Case-Control Study Results
Exposure Cases 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
Dole
prepackaged
lettuce salad 9/10 5/23 10.1 1.5–67.3 0.002
*OR = odds ratio
†
CI = confidence interval

22. E. coli O157:H7 Cases Associated
with Dole Prepackaged Lettuce
7
Number of Cases
6
5 Case-control study implicated Dole salad.
4
Case-control study initiated.
3
2 Initial cluster of 3 isolates
among MN residents
1 identified.
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 Onset 2005

23. E. coli O157:H7 Cases Associated
with Dole Prepackaged Lettuce
CDC, FDA notified.
7
Number of Cases
6
5 Case-control study implicated Dole salad.
4
Case-control study initiated.
3
2 Initial cluster of 3 isolates
among MN residents
1 identified.
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 Onset 2005

24. E. coli O157:H7 Cases Associated
with Dole Prepackaged Lettuce
CDC, FDA notified.
7
Number of Cases
6
5 Case-control study implicated Dole salad.
4
Case-control study initiated.
3
2 Initial cluster of 3 isolates
among MN residents
1 identified.
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 Onset 2005

25. E. coli O157:H7 Cases Associated with
Dole Prepackaged Lettuce (N=26)
Minnesota
Additional states
Number of Cases
7
6
5 OR
4
3
2 WI
1 WI
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 Onset 2005

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

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

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

29. Why Epidemiologic Links May Not be
Identified for Cases in a PFGE Cluster
• Cases have
imperfect recall
• Common exposures
can be difficult to link
(e.g., eggs, chicken)
• Secondary
transmission
• Cross-contamination
exposure
• There isn’t a
common source

30. CDC 2005 Cluster Investigations
E. coli O157 Salmonella
Patterns Submitted 5,376 29,168
Clusters Identified 67 176
Multi-state Clusters 36 152
Epi Investigation 19 30
Vehicle Implicated 4 8
Regulatory Activity 4 8

31. Questions?