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Technology Trace Back: Keys to Tracking Foodborne Outbreaks

This story was originally published on Oct. 6, 2018. As part of MedPage Today‘s year-end review of 2018’s top stories, we are republishing it along with an update on progress in stemming the tide of foodborne illness outbreaks.

SAN FRANCISCO — A mix of better technology and good, old-fashioned detective work helped identify some of the most prominent foodborne illness outbreaks of 2018, experts said here.

But as the technology to detect outbreaks improved, some uncovered weaknesses within the process that required attention from industry and the FDA.

Experts from the CDC examined lessons learned from these outbreaks at a late-breaker session at IDWeek, with joint sponsorship by the Infectious Diseases Society of America (IDSA), the Pediatric Infectious Diseases Society (PIDS), the Society for Healthcare Epidemiology of America (SHEA), and the HIV Medicine Association (HIVMA).

Robert V. Tauxe, MD, MPH, of the CDC in Atlanta, characterized the recent array of outbreaks as “good news” because every outbreak helps to make things safer.

With advances in culture-independent diagnostic testing, which has enabled rare infections to be reported more frequently, improved trace back using better food industry data systems, and the transition of molecular subtyping to whole-genome sequencing, Tauxe said the concept of an “outbreak” is broadening.

But all outbreaks seem to start with an epidemiologic investigation (an aspect in which Tauxe characterized as “they ate the same thing”). Nowhere was that more evident than in the case of Salmonella infection linked to Honey Smacks cereal, which started with a cluster of 12 older women who became ill with Salmonella Mbandaka. But the case turned on open-ended, single person interviews with six people.

“Two mentioned they had eaten Honey Smacks cereal. We went back to the other four and found that eating Honey Smacks was also likely. In the other cases, 75% ate Honey Smacks,” Tauxe said. “When the company was approached, they had found Salmonella in their facility.”

In fact, Tauxe mentioned that of the 135 infections in 36 states, patients were a median age of 57 and almost 70% were women.

He said that it will be important to understand what happened in the manufacturing plant, but that the FDA has already taken steps to try to prevent it from happening again.

“There’s a new regulation that the FDA put out for processed foods. One of the key parts of that is environmental monitoring within the plant, and acting on it when you find things,” he told MedPage Today. “The FDA is in the process of ramping up implementation of this in plants of various sizes. Salmonella in cereal is a big deal.”

An epidemiologic investigation also aided what Tauxe dubbed as “the summer of cyclosporiasis” linked to certain vegetable trays and salad mixes. He estimated there was “over a ten-fold number” of cases as those reported just 2 years ago, thanks to advances in culture-independent diagnostic testing.

While investigating, the FDA found Cyclospora in domestically grown produce, which Tauxe said marked the first time the agency found a parasite for food produced in the U.S.

He called it a “game-changer,” adding that now, “we have to think about how contamination is occurring in the U.S.”

Of course, no discussion of contaminated produce would be complete without mentioning the biggest outbreak of foodborne illness this year in terms of cases — the Shiga-toxin producing E. coli outbreak linked to romaine lettuce. In his presentation, Christopher Braden, MD, also of the CDC, detailed the lessons learned from that investigation.

Based on the investigation, it appeared water may have been contaminated from a nearby cattle stream, and that potentially contaminated water may have been widely distributed over the fields by a pesticide truck. However, “we do not have definitive evidence of how E. coli got from the cattle lot into the stream,” Braden emphasized.

Complicating the matter, there was a freeze in February, Braden said, which could have damaged the crops and “damaged leaves are more susceptible to infection by human pathogens.”

Investigators were stymied throughout this outbreak by a complicated distribution chain that made trace back difficult; the fact that trace back went to many fields and was not just a single contamination event; and the lack of growing location on packaging complicated the consumer/retail warnings.

But the industry appears to have taken action against this happening again. Braden said they put together a food safety task force and came up with recommendations that are part of a “leafy green marketing agreement.”

Such recommendations include increasing the distance from cattle operations where growers can actually produce food, and treating water potentially at risk of contamination, before it’s applied in a way to potentially contaminate what people eat, he said.

Tauxe and Braden disclosed no relevant relationships with industry.