By Donna Campisano, specialist, Communications, APHL

Last summer, Centers for Disease Control and Prevention (CDC) began investigating a multistate outbreak of Listeria monocytogenes, which, to date, has killed ten people and caused 59 to be hospitalized across 19 states. That makes it the largest Listeria outbreak this country has seen since 2011.

Listeriosis is a foodborne illness caused by Listeria monocytogenes that can result in severe sickness, miscarriages and death; it strikes the elderly, pregnant women and those with a weakened immune system particularly hard. CDC notes that Listeria are “hardy germs” that can survive refrigerated temperatures and linger on surfaces such as counters, deli meat slicers, machinery and hands. Determining where a person may have come in contact with Listeria can be especially problematic, seeing as it can take 10 weeks for people to show symptoms of listeriosis after being infected.

Disease detectives get to work

Six of the people sickened with Listeria monocytogenes last summer lived in Maryland, which prompted public health officials there to spring into action.

Epidemiologists at the Maryland Department of Health (MDOH) interviewed patients and their families to try and detect common denominators. And deli meats—particularly those manufactured by Boar’s Head and sliced at the deli counter—soon emerged as a prime suspect.

“By that point, the investigation centered around about a half dozen different deli items,” said Sin Urban, PhD, division chief in the Division of Environmental Sciences at MDOH Laboratories Administration, the state’s public health laboratory. “And one of them was liverwurst. We were also noticing that the median age of patients was 78. This got one of our epidemiologists thinking: maybe liverwurst is something older people are going to eat more often than younger people. Maybe liverwurst is our culprit.”

With that hunch in mind, the MDH Office of Food Protection’s Rapid Response Team coordinator went to the grocery store where one of the patients said they had bought deli meat. She purchased three unopened products—a 3.5-pound package of Boar’s Head liverwurst along with a Boar’s Head turkey item and barbecue loaf.

“With this being a national outbreak, it wasn’t likely that the meat was contaminated via a slicer, in peoples’ homes or from an individual delivery system,” Urban, pictured above, right, said. “Our idea was that the actual food item itself was contaminated, so we needed to find an unopened product that we could then test for Listeria.”

An APHL-CDC Public Health Laboratory fellow helps crack the case

Knowing that Listeria wouldn’t be present uniformly throughout each product, the scientists at the Maryland Public Health Laboratory in Baltimore decided to take each meat and cut it into sections. The sections of each meat product were then pureed in a blender to distribute any potential bacteria throughout.

Once blended, the team would be able to do molecular testing on the samples, first looking for proteins associated with Listeria.

That’s where APHL-CDC Public Health Laboratory Fellow Jesus Bedolla, pictured above, left, entered the picture.

Only a few months into his fellowship, Bedolla took quickly to the lab’s Listeria testing methods (partly because of his prior experience in food microbiology), and when the outbreak occurred, it was coincidentally his turn to test incoming samples.

On Friday, July 19, Bedolla began enriching the samples (a method that helps the bacteria grow) and then returned on Saturday, July 20 for a second enrichment process. When he returned to the lab on Sunday, he performed a protein-based screen on the samples. The liverwurst turned up presumptive positive for Listeria while the turkey and barbeque loaf were both negative. More testing—including diligently isolating the Listeria strain in pure form and whole genome sequencing—determined that not only did the liverwurst contain Listeria monocytogenes, it contained the same strain that was making people sick.

Case not closed

On July 25, less than a week after the initial samples were sent to the lab, data was sent to US Department of Agriculture’s Food Safety and Inspection Service which announced that Boar’s Head was recalling its liverwurst product produced at its Jarratt, Va., plant (which had been cited for numerous noncompliance issues and where the Listeria-contaminated liverwurst had originated). The recall was expanded to include other Boar’s Head products produced on the same line and on the same day as the liverwurst. All in all, 7 million pounds of ready-to-eat Boar’s Head meat and poultry products were recalled.

“The urgency with which we got this recall done was fantastic. It was a great experience,” Bedolla said. “We’ve worked deli meat foodborne illness cases before, but we’ve never been able to pinpoint a source,” added Kristen Lozinak, Bedolla’s mentor and supervisor of food microbiology and media laboratories at MDOH. “Kudos to Jesus and the lab for being able to do it this time.”

“Every day saves lives.”

About half of foodborne disease cases are never solved, said Urban, who also serves as Bedolla’s mentor. And when they are, it can take months to unearth the cause. Cracking this Listeria case, which took little more than a week, involved a lot of careful thinking and analysis.

“There’s no magic instrument that we had that other labs didn’t,” Urban said. “This involved a lot of people being diligent and putting their heads together and being very thoughtful about the detective process. Being able to act quickly and do the testing and identify the source is really, really key in these types of outbreaks. Every day saves lives.”

What now?

About six weeks after the outbreak began, Boar’s Head announced it would stop manufacturing liverwurst and has shuttered indefinitely its Jarratt, VA, plant where the tainted products were produced.

In a statement, the company said it “regrets and deeply apologizes” for the Listeria monocytogenes contaminations of its liverwurst and says “comprehensive measures” are being implemented to prevent other issues in the future.

But while the case may be solved, consumers should still be vigilant.

Some of the recalled products can have a long shelf life, and CDC recommends that consumers discard or return to the store any Boar’s Head meats with “EST-12612” or “P-12612” on their labels.

Symptoms of listeriosis—which can start as late as 70 days after eating the contaminated food—can include fever, muscle aches, confusion, headache, stiff neck and convulsions. See your healthcare provider if you experience any of these symptoms.

The post Inside the Country’s Worst Listeria Outbreak in 13 Years appeared first on APHL Blog.

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