Investigating Foodborne Disease Investigating Foodborne Disease Outbreaks: The CDC PerspectiveOutbreaks: The CDC Perspective

Ian Williams, PhD, MSChief, Outbreak Response and Prevention Branch

Division of Foodborne, bacterial and Mycotic DiseasesCenters 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

• 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

The Spectrum of Foodborne Disease OutbreaksThe Spectrum of Foodborne Disease Outbreaks

These changes make coordination among multiple states and agencies, and countries even more important than before

Public Health Infrastructure in the United StatesPublic 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

Federal Roles Federal Roles

• CDC:– Disease surveillance– Outbreak detection and

investigation– Education and training of

public health staff

• FDA & FSIS:– Food safety policies– Inspection and enforcement– Product recall and traceback– Investigation of farm and

production facilities

Problem identification Risk assessment and management

Source implication Source assessment

Foodborne Disease Outbreak InvestigationsFoodborne Disease Outbreak Investigations

• Goals of investigations– Immediate control of outbreak and prevention of illnessesImmediate control of outbreak and prevention of illnesses– Provide opportunities to identify gaps in food safety Provide opportunities to identify gaps in food safety

systemssystems

• 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

Cycle of Foodborne Disease Control and Prevention

Surveillance

Epidemiologic Investigation

AppliedResearch

Prevention Measures

Cycle of Foodborne Outbreak Control & Cycle of Foodborne Outbreak Control & Prevention: Stages of an InvestigationPrevention: Stages of an Investigation

Surveillance

Epidemiologic Investigation

AppliedResearch

Prevention Measures

Detecting a cluster (increase # of infections above baseline for time period)

National Surveillance for Bacterial National Surveillance for Bacterial Foodborne InfectionsFoodborne Infections

• Reports to CDC of suspected outbreaks by state and local health departments

• Laboratory-based surveillance of clinical isolates

– Serotype results

– PulseNet

What is PulseNet USA?What is PulseNet USA?

• National network of >75 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

PulseNet Data Analysis: Searching for ClustersPulseNet Data Analysis: Searching for Clusters

Cluster of indistinguishable patterns

•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

Cycle of Foodborne Outbreak Control & Cycle of Foodborne Outbreak Control & PreventionPrevention

Surveillance

Epidemiologic Investigation

AppliedResearch

Prevention Measures

CDC’s OutbreakNet TeamCDC’s 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

Cycle of Foodborne Disease Control & Prevention: Cycle of Foodborne Disease Control & Prevention: Stages of an Outbreak InvestigationStages of an Outbreak Investigation

Surveillance

Epidemiologic Investigation

AppliedResearch

Prevention Measures

Detecting a cluster in the first place

- Generating hypotheses

- Testing hypotheses

- Reconstructing how and where contamination is likely to have occurred

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!

Hypothesis-Generating TracebacksHypothesis-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

Testing HypothesesTesting 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 < 5%)• Strength of association (No fixed rule)• Dose-response relationship (Supports if present)

• Plausibility of association• Repeat process as necessary

Cycle of Foodborne Disease Control & Prevention: Cycle of Foodborne Disease Control & Prevention: Stages of an Outbreak InvestigationStages of an Outbreak Investigation

Surveillance

Epidemiologic Investigation

AppliedResearch

Prevention Measures

Prevention MeasuresPrevention Measures

Epidemiologic Investigations

Traceback Investigations

Environmental Assessments

Laboratory Investigations

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

http://www.cdc.gov/foodborneoutbreaks/