CDC identifies potential outbreaks by monitoring the information it receives from various sources. For many pathogens, states are required to report illness and the pulse-field gel electrophoresis (PFGE) patterns of the pathogens recovered from the patients. These PFGEs are uploaded into the CDC database. A cluster of a particular pattern or a new pattern will receive attention.

Alternatively, a state may report a cluster of illnesses with the same PFGE pattern to CDC. Finally, the PFGEs of positive government samples generated under a regulatory scheme (Food Safety and Inspection Service (FSIS) pathogen testing) or a baseline (such as the National Antimicrobial Resistance Monitoring System (NARMS)) might match the PFGE of case patients uploaded within the last 90 days. No matter how discovered, when a number of illnesses appear to be related, the investigation stage begins.

In conducting the investigation, CDC will contact the states reporting the illnesses for more information, especially the patient’s food history (what they ate and where). In determining whether a common food is likely, CDC compares the percentage of case patients consuming a particular food as opposed to the normal consumption for that food. For example, spinach might be consumed by 50 percent of the population in a given week, but if 90 percent of the case patients consumed spinach, it could be deemed a likely source. If product testing has occurred (such as leftover product in the consumer’s home or random regulatory sampling), this will be factored in. Importantly, neither CDC nor FSIS requires a product positive to identify a likely source.

After its preliminary review, CDC will contact the regulatory agency with jurisdiction over the likely food source. For meat and poultry, FSIS is notified, initially when the food source “possibly” could be a meat/poultry product, and then again if CDC determines the illnesses were “likely” caused by a particular meat or poultry product. With this latter notification, FSIS initiates its own investigation.

At this stage, representatives from FSIS’ Office of Investigation, Enforcement and Audit (OIEA) will go to the “establishments of interest” to request shipping records to determine if the establishment’s products were available at the outbreak locations and the production dates of those products. OIEA will also contact the case-patients to determine whether any remaining product is available for sampling, or whether the purchases might be documented through shopper cards. FSIS might also direct the inspector at the establishment to draw targeted samples for analysis.

FSIS will request an establishment recall certain product when the results of the investigation demonstrate:

• There were related illnesses (an outbreak) as determined by the PFGE,
• The evidence supports the conclusion that the likely source of the illness was a specific meat or poultry product,
• The establishment produces that specific product, and
• Specific production of that establishment’s product was available to the case patients at the time and location of the illnesses.

All elements have to be present.

That, in a nutshell, is how outbreaks lead to recalls.