Investigating Foodborne Disease Outbreaks: The CDC Perspective

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Investigating Foodborne Disease Outbreaks The
CDC Perspective
Ian Williams, PhD, MS Chief, Outbreak Response
and Prevention Branch Division of Foodborne,
bacterial and Mycotic Diseases Centers for
Disease Control and Prevention
The findings and conclusions in this presentation
are those of the author and do not necessarily
represent the views of the Centers for Disease
Control and Prevention
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The Spectrum of Foodborne Disease Outbreaks

• Old focal scenario
• Large number of cases in one jurisdiction
• Detected by affected group
• Local investigation
• Local food handling error
• Local solution

• New dispersed scenario
• Small numbers of cases in many jurisdictions
• Detected by lab-based subtype surveillance
• Multistate/Country investigation
• Industrial contamination event
• Broad implications

These changes make coordination among multiple
states and agencies, and countries even more
important than before
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• Public Health Infrastructure in the United States

• The county or city health department
• The front line of public health
• The State health department
• Epidemiologists
• Laboratorians
• Sanitarians
• The federal agencies
• Risk identification agency CDC (non-regulatory)
• Risk management/regulatory agencies FDA, USDA,
  EPA
• "Tiered response" to emergencies
• CDC provides back-up to States epidemiologists,
  laboratory support, coordination

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Federal Roles

• FDA FSIS
• Food safety policies
• Inspection and enforcement
• Product recall and traceback
• Investigation of farm and production facilities

• CDC
• Disease surveillance
• Outbreak detection and investigation
• Education and training of public health staff

Problem identification
Risk assessment and management
Source implication
Source assessment
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Foodborne Disease Outbreak Investigations

• Goals of investigations
• Immediate control of outbreak and prevention of
  illnesses
• Provide opportunities to identify gaps in food
  safety systems
• Outbreak epidemiology changing
• Globalization, centralization, industrialization
• Number of possible outbreaks detected has grown
  substantially
• Effective investigations key to reducing burden
  of foodborne disease
• Identify food vehicles and factors which lead to
  outbreaks

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Cycle of Foodborne Disease Control and Prevention
Surveillance
Applied Research
Epidemiologic Investigation
Prevention Measures
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Cycle of Foodborne Outbreak Control Prevention
Stages of an Investigation
Surveillance
Detecting a cluster (increase of infections
above baseline for time period)
Applied Research
Epidemiologic Investigation
Prevention Measures
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National Surveillance for Bacterial Foodborne
Infections

• Reports to CDC of suspected outbreaks by state
  and local health departments
• Laboratory-based surveillance of clinical
  isolates
• Serotype results
• PulseNet

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What is PulseNet USA?

• National network of gt75 public health and
  regulatory laboratories
• Perform molecular typing of foodborne
  disease-causing bacteria
• Current method is pulsed-field gel
  electrophoresis (PFGE)
• Create DNA fingerprints
• Share DNA fingerprints electronically
• DNA fingerprints are kept in dynamic database
  at CDC
• available on-demand to participants

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PulseNet Data Analysis Searching for Clusters

• State health depts submit patterns electronically
• CDC searches for similar patterns in past 2-4
  months
• CDC compares patterns visually
• When cluster identified, PulseNet contacts
  epidemiologists

Cluster of indistinguishable patterns
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Cycle of Foodborne Outbreak Control Prevention
Surveillance
Applied Research
Epidemiologic Investigation
Prevention Measures
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CDCs OutbreakNet Team

• Supports a national network of epidemiologists
  and other public health officials who investigate
  outbreaks of foodborne, waterborne, and other
  enteric illnesses in the United States
• Collaboration between CDC and
• U.S. State and local health departments
• U.S. Department of Agriculture (USDA)
• U.S. Food and Drug Administration (FDA)
• Works in close partnership with PulseNet
• The national molecular subtyping network for
  foodborne disease surveillance
• Helps ensure
• Rapid, coordinated detection response to
  multi-state enteric disease outbreaks
• Promotes comprehensive outbreak surveillance

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Cycle of Foodborne Disease Control Prevention
Stages of an Outbreak Investigation
Surveillance
Detecting a cluster in the first place
- Generating hypotheses
Epidemiologic Investigation
Applied Research
- Testing hypotheses
- Reconstructing how and where contamination is
likely to have occurred
Prevention Measures
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Hypothesis Generating Interviews

• Strategies include
• Interviews with structured questionnaire with
  many food items trolling, trawling, or
  shotgun
• Intensive open-ended interviews about food eaten
  in 7 days before illness began
• In-depth interview with people in their homes,
  including refrigerator, pantry
• Some combination of the two
• All should be done the same way
• A food product is not the source of all
  outbreaks!

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Hypothesis-Generating Tracebacks

• Data on product distribution production can be
  critical in development of hypothesis
• Evaluate potential sources
• Ways to obtain this information
• State Departments of Agriculture
• Regulatory agencies
• Involvement before a product has been implicated
  can pose unique problem for some agencies

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Testing Hypotheses

• Systematically compare exposures of ill and those
  who remained well
• Two structures of investigation
• Illness in a defined group (cohort) after an
  event interview whole group about exposures and
  subsequent illness
• Illness in cases and controls interview the ill
  people and comparable healthy persons (controls)
  about preceding exposures
• Measure statistical association of illness with
  each exposure
• Direction of association (Should be
  positive)
• Probability of chance alone (Should be lt 5)
• Strength of association (No fixed rule)
• Dose-response relationship (Supports if present)
• Plausibility of association
• Repeat process as necessary

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Cycle of Foodborne Disease Control Prevention
Stages of an Outbreak Investigation
Surveillance
Applied Research
Epidemiologic Investigation
Prevention Measures
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Prevention Measures
Traceback Investigations
Environmental Assessments

• Epidemiologic
• Investigations

Laboratory Investigations
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http//www.cdc.gov/foodborneoutbreaks/
The findings and conclusions in this presentation
are those of the author and do not necessarily
represent the views of the Centers for Disease
Control and Prevention