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STEC Pathogens Are A Food Safety Challenge

Emerging STEC pathogens pose a challenge to industry.

June 1, 2011

6 Min Read
STEC Pathogens Are A Food Safety Challenge

It was just short of 20 years ago that beef producers had to familiarize themselves with the term O157:H7 and learn about the ramifications of the pathogen. Now there’s a new set of letters and numbers related to food safety that need similar attention – STEC.

STEC – or Shiga toxin-producing E. coli – includes O157:H7, but represents a broader continuum of both benign and virulent germs that researchers, government officials and industry leaders are working hard to overcome. While hundreds of non-O157 STEC exist, they vary considerably in their severity, with some possibly as dangerous as O157:H7, and others presenting no problems.

“O157:H7 is certainly the most famous, and it’s very pathogenic,” says Terry Arthur, PhD, a microbiologist with the USDA Agricultural Research Service’s Meat Safety & Quality Research Unit in Clay Center, NE. “At the other end of the spectrum are those that probably won’t cause illness. In the middle there’s a breakpoint, and where that breakpoint is we don’t know.”

Non-O157 STEC (often pronounced ESS-teck) linked to foodborne illness in the U.S. include E. coli O26, O45, O103, O111, O121 and O145. While little is known about these strains, a 2008 outbreak of E. coli O111 from unknown sources in Oklahoma resulted in the hospitalization of 70 people and one death.

Arthur says that while O157:H7 has a genetic quirk that makes it easy to identify and trace, the same isn’t yet true for other STEC. “Methodologies aren’t as sensitive, specific and rapid as they are for O157:H7,” Arthur says. “It really is a needle-in-a-haystack situation.”

Raj Mody, MD, Lt. Commander in the U.S. Public Health Service, Centers for Disease Control (CDC) Enteric Diseases Epidemiology Branch, agrees. “For O157:H7, we’re blessed with a unique detection method,” he says. Because it’s been more difficult to detect other STEC, there is a “paucity of data” on how people acquire these infections, including the types of foods most responsible. “We need to better understand the virulence factors that lead some of these STEC to cause severe illness,” Mody says.

He adds there are about 176,000 food-borne STEC infections annually in the U.S., with non-O157 STEC responsible for about two-thirds of them. However, those non-O157 STEC are responsible for only 10% of the STEC hospitalizations, with the other 90% the result of E. coli infection. (CDC says E. coli O157:H7 results in more than 2,100 hospitalizations annually, compared to 19,000 for salmonella, and 14,000 for norovirus.)

Though STEC infections aren’t as common as other foodborne illnesses, the hemolytic uremic syndrome related to O157:H7 and other virulent forms of STEC is potentially deadly. At the same time it causes human illness, it’s also compromising the industry’s food safety reputation. For both reasons, the industry has been especially aggressive in identifying and combating pathogens in beef (see the Beef Industry Safety Summit sidebar).

Pre-harvest focus

Interventions to reduce pathogens in packing plants have steadily reduced pathogen levels and outbreaks. Research to develop and validate many of these interventions was funded by beef producers through the beef checkoff program. Now research attention is being redirected to the pre-harvest level to see what can be done to control STEC and other pathogens at the source.

Tom Besser, DVM, a professor and researcher in Washington State University’s College of Veterinary Medicine, has studied E. coli for more than 20 years at pre-harvest. He admits “we still don’t understand a lot” of what’s going on with non-O157:H7.

“There’s not a single, specific, strong recommendation we can make for producers” when it comes to reducing E. coli fecal shedding in cattle. “Producers just have limited control on microbiology in their animals, and pre-harvest interventions that will eliminate fecal shedding have yet to be discovered,” he says. “But there are quite a few irons in the fire.”

Three of those are sodium chlorate – fed the last few days before harvest; vaccines administered to cattle; and the use of antimicrobial phages (viruses that target specific pathogens) sprayed onto cattle prior to harvest.

Jeff Clausen, a cattle feeder and farmer from Carson, IA, and chairman of the industry’s checkoff-funded Beef Safety Committee, says he knows a silver bullet to the challenge isn’t possible, but is happy work is being done on the problem.

“It’s a good feeling to know we have really smart people in the position to research these things,” he says. “On the producer level, we need to find something that’s very effective, then find a way to pay for it.”

Clausen says producer-funded research through the beef checkoff “is one of the best investments we’ve ever made. We are finding the gaps (to knowledge), and developing solutions.”

Besser says that even though checkoff investments usually don’t represent the majority of research funding, those investments have been vital to the success in E. coli research. “They make it possible to get funding elsewhere, create a track record and play a key role” in funding in general, he says.

Government interest

Currently it’s unclear if plans exist to specifically regulate emerging STEC pathogens. It appears the top priorities – in this case, O157:H7 – will continue to receive government focus as regulatory agencies assess the risk of non-O157 STEC.

And there may be a silver lining in dealing with this cloud of bacteria. It may not be necessary to have a different defense for each STEC identified.

“If you focus on the top six (STEC), you might come up with something that provides cross protection,” Arthur says. For instance, O157:H7 is “very representative” of O26 and O111, he says.

“You can’t test them all,” Arthur says. “You have to pick and choose. O157:H7 probably models the diversity (of STEC) as well as any of them.”

Besser says lessons learned in the fight against O157:H7 have given the industry a head start. “What we know about controlling O157:H7 will help us in our work against non-O157,” he says. That work suggests no initial change in management or new interventions – even though we may see proportionally more recalls as government and industry become more adept at identifying and tracing other strains.

At the very least, producers will have no choice but to pay attention. “Producers can expect to be hearing more and more about STEC in the near future as more and more (human) infections are diagnosed,” Mody says.

Sidebar: Beef Industry Safety Summit

STEC was just one of the topics discussed by more than 240 beef industry leaders, researchers and government officials at the 9th Annual Beef Industry Safety Summit, in Dallas, TX, in early March. Participants welcomed the opportunity to learn more about the status of U.S. beef safety and share ideas for minimizing human foodborne health risks.

The first Beef Industry Safety Summit was hosted by the Beef Industry Food Safety Council (BIFSCo) in January 2003 in San Antonio, and attracted 200 participants. Attendance at this year’s event was a record.

The Beef Industry Safety Summit is coordinated by BIFSCo, which represents every segment of the beef industry and has been responsible for implementation of many innovations that advance U.S beef safety. Funded in part by the beef checkoff, BIFSCo was established in 1997 to develop industry-wide, science-based strategies to address food safety issues in beef. Among its contributions to food safety are best practices documents to serve as roadmaps for making beef a safer product.

Next year’s Beef Safety Summit will take place in Tampa, FL. For more on the event, visit www.bifsco.org.

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