How FDA Investigators Uncovered Source of Salmonella Tied to Illness-Causing Eggs
How FDA Investigators Uncovered Source of Salmonella Tied to Illness-Causing Eggs
By: Erin Peabody
On a muggy afternoon last August in America’s heartland, four investigators with FDA’s frontline field staff, known as the Office of Inspections and Investigations (OII), pulled up to the entrance of a local poultry farm.
The investigators sprayed the vehicle’s tires down with disinfectant, then donned full body coveralls, boot coverings, gloves, and N-95 masks. After loading notebooks and a slew of sampling kits into their packs, the foursome headed towards the poultry house ahead.
At the same time, dozens of Americans were falling sick, experiencing diarrhea, fever, and stomach cramps. Some had to be hospitalized, their symptoms were so severe. The cause? A strain of Salmonella whose exact origin was still unknown.
FDA, CDC, and state officials, who routinely share data and coordinate response during emergency foodborne outbreaks, believed that evidence collected so far from sick patients and other sources pointed to a single culprit: a small Midwestern poultry farm.
Food Safety Responders
OII investigators, also known as consumer safety officers, are specially trained to respond to public health emergencies. They know what sanitation steps are required of industry, including, in the case of hen houses, regular environmental testing for Salmonella Enteritidis (SE)—a highly problematic disease occurring in poultry that’s also the leading cause of Salmonella illness in humans tied to the consumption of shell eggs.
FDA food investigators know how important it is to stay ahead of pervasive pathogens like SE, which can sweep through poultry houses like wildfire and taint entire clutches of eggs.
They’re also well-versed in collecting the scientific evidence needed to inform the agency’s crucial next steps—whether that’s recommending the farm issue a voluntary recall that leads to the removal of products from grocery store shelves, or using some other authority to shield the public from harm.
A supervisory investigator at a local FDA district office helped coordinate the field response to the Salmonella outbreak that was rapidly unfolding. As it turned out, he’d need all the support he could get.
Cracked Open
The problem? What public health officials had initially believed was just one farm responsible for causing the outbreak turned out be a much bigger affair.
As OII learned—thanks to the help of its dedicated state partners—26 other poultry farms regularly supplied eggs to the small farm at the center of the investigation.
“The farm was not just a hen-laying operation,” said the supervisory investigator. “It was a packing facility, too, bringing in and commingling shell eggs from numerous other small farms in the area.”
The field investigators’ traceback assignment—to follow the path of the pathogen—had just swelled exponentially.
With more help needed, OII’s division management put in calls to any available investigators in the country with experience conducting on-farm egg inspections.
OII investigators are specially trained based on the commodity they oversee. That might be human foods, animal foods (like pet food), drugs, medical devices, vaccines and other biologics, or any other product whose safety and effectiveness is overseen by the FDA.
“The response was incredible,” said the supervisory investigator. “In addition to staff coming in from nearby district offices, we also had investigators and other specialists fly in from across the nation to help us out.”
Drag Swabs and Sponge Sticks
With heightened biosecurity protocols in place, the investigators needed to quarantine for a week between farm inspections, another reason additional inspectional reinforcements were needed.
The quarantine precautions they heeded—just like the body coverings, gloves, and masks they wore—weren’t only intended for personal protection, but for preventing the spread of bacteria and viruses, including avian flu, from one poultry farm to another too.
The investigators’ primary task was to collect samples—namely, of chicken manure. In the hen houses, that meant dragging a specially treated swab, held by a cord, back and forth across the floor. In the egg packaging facility, they used small sponges, held by a small wand, to dab and wipe at surfaces.
OII investigator teams spent hours at a time inside hen houses rife with chicken dander, waste, and ammonia gas.
Once finished, they sent all carefully bundled samples to FDA laboratories across the country for Whole Genome Sequencing, or WGS. WGS was key, as DNA analysis was critical to determining if genetic material in the chicken manure samples matched the specific strain of Salmonella that was causing illness in patients.
Harmful Eggs Pulled from Shelves
The FDA laboratories confirmed what investigators and public health officials had suspected: Samples collected from the poultry house and egg-packing facility located at the farm identified at the start the investigation were a match to the outbreak strain.
The labs’ analysis also tied the culprit strain to another poultry house supplying eggs to that farm, and a potentially related strain to yet another poultry house in the area.
As a result of these findings—and thanks to vital contributions from FDA’s local recall coordinator, emergency response coordinator, and experts on the Coordinated Outbreak Response and Evaluation team—the farm initiated a recall and ceased all production and distribution of its eggs.
Tens of thousands of eggs originating from the farm and its packing operation were pulled from grocery shelves and retail outlets, eliminating further risks to consumers.
Dedication to Mission
Still, OII investigators closely involved in the inspection blitz were frustrated they couldn’t do more—and faster—to stop the outbreak.
One thing they noted, having observed conditions inside numerous hen houses: If all poultry farms, followed SE control measures—including regular environmental monitoring for the pathogen—chances of another Salmonella-based outbreak from eggs would likely meaningfully diminish.
The investigators working on the case devoted entire weeks, and weekends, to tracking down the source of the Salmonella in eggs that was making people sick.
As one investigator noted though: “We know how important these efforts are to keeping Americans safe and healthy. It’s why we signed up for this work.”
**For more on how the FDA protects consumers from foodborne illness in shell eggs, see the agency’s Egg Guidance and Regulations. Its Compliance Guide tells egg producers how to prevent Salmonella Enteritidis (SE) from contaminating eggs on the farm and from further growth during storage and transportation. **