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

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

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

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 identificationRisk assessment and management Source implicationSource assessment

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

Cycle of Foodborne Disease Control and Prevention Surveillance Epidemiologic Investigation Applied Research Prevention Measures

Cycle of Foodborne Outbreak Control & Prevention: Stages of an Investigation Surveillance Epidemiologic Investigation Applied Research Prevention Measures Detecting a cluster (increase # of infections above baseline for time period)

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

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 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 & Prevention Surveillance Epidemiologic Investigation Applied Research Prevention Measures

CDC’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: Stages of an Outbreak Investigation Surveillance Epidemiologic Investigation Applied Research 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 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 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: Stages of an Outbreak Investigation Surveillance Epidemiologic Investigation Applied Research Prevention Measures

Prevention 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