Special Report E coli testing presents challenges

by Bryan Salvage
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WASHINGTON — Testing food products to ensure food safety is a complex issue involving many factors. There are three major components meat processors should consider when testing, according to Jim Hodges, executive vice-president of the American Meat Institute and president of the A.M.I. Foundation.

"One is — do we have an effective sampling program where we’re growing samples that represent the product we want to find out something about?" he said. "Two, is our lab analysis accurate? Three and probably most importantly, what’s the appropriate response to findings as many folks in our industry say — ‘it’s not what you find, it’s what you do when you find it.’

The U.S. beef industry has devoted enormous resources to preventing E. coli O157:H7 in ground beef. "Testing is a powerful tool if used right to drive meaningful food safety improvements," Mr. Hodges said. "But fundamentally, it is prevention that is the key to producing safe food. Testing tells a plant what works, what does not work and what needs to be done next to improve the process. But it does not make food safe."

Mr. Hodges went on to explain most ground beef is made from beef trimmings, which are wholesome, U.S.D.A.-inspected parts that make up a significant portion of the beef carcass. "About half of the beef consumed in the U.S. is in ground form," Mr. Hodges said. "Different lean and fat trimmings are blended together to formulate products that have different lean and fat contents. Consumers like different grinds of product and these different blends give consumers several choices to fit their personal desires and their family dietary needs."

Industry-wide testing has unquestionably improved beef safety, Mr. Hodges stressed. Testing provides feedback to monitor and maintain sanitary slaughter procedures and to validate the effectiveness of microbial interventions.

"Industry conducts more than 1 million tests for E. coli O157:H7 each year. But testing is only one part of a total systems approach to food safety," Mr. Hodges said.

But testing is not a silver bullet. Testing has limitations.

"A negative test does not always mean that bacteria are not present in the product," he added. "One way to visualize this concept is to think of one colored bead that represents E. coli contaminated product in a bowl of 200 or 300 white beads that represent the product that does not contain O157. We chose those numbers of white and red beads because of the prevalence of E. coli O157:H7 is very low.

"It has stayed below one half of 1% for many years," he continued. The current rate this year is 0.32%, or one-third of 1% prevalence rate."

After taking the sample of ground beef, ground beef testing occurs in a laboratory where preliminary test results are usually obtained in about 24 hours. "It’s important to understand it’s not just the sample that you draw — it is the analytical methods must be accurate, sensitive and precise," Mr. Hodges said. "U.S.D.A. requires in our testing programs that the analytical methods be the equivalent to the methods they use in their own laboratories."

Mr. Hodges explained testing destroys ground beef...it is destructive to sample. "The only way to make sure ground beef is E. coli-free is to test it all," he added. "We do not use the term E. coli-free because we cannot verify it is so. If you think about sampling on a very basic level and we use our bowl of beads as an example, we can sample the population several times yet not find the contaminated product because the prevalence of E. coli O157:H7 is usually very, very low."

Sampling has its share of challenges. "Every sampling scheme results in some probability that you’re going to get the wrong answer when you’re looking for the correct result," Mr. Hodges said. "The more samples [taken] increases the probability of detecting a contaminated lot. But if you have a very low level of contamination, the probability of detecting a contaminated lot is much less with the same number of samples."

Mr. Hodges explained that the 'N' in the term N-60 is what statisticians use to represent the number of samples. So, N-60 is 60 sample units, which is the unit that’s normally used to test beef trimmings.

Lots that are more highly contaminated can very effectively be removed from the ground beef supply within 60 testings, Mr. Hodges said. "But it does not get everything. Testing cannot guarantee E. coli -free product," he warned.

A "negative" doesn’t necessarily mean there is not contaminated product in the lot. "The only thing we can definitively say is that the sample did not contain O157:H7 — and that’s assuming that the analytical method was sensitive enough to find even one cell in the product," Mr. Hodges said. "The sensitivity of analysis is normally the ability to detect one cell in 65 grams, which is the sensitivity employed by Food Safety and Inspection Service analytical methods."

Although more samples reduce the probability of accepting a contaminated lot, a very low level of contamination still makes it very difficult to detect that contaminated lot, he added.

Another way to look at the complexity of issues surrounding sampling is the number of samples needed for a 95% confidence level to detect contamination increased exponentially in order to detect lower and lower contamination rates. It takes very, very large numbers to detect low contamination rates.

"The bottom line is negatives are a good sign, but there's no guarantee that E. coli does not exist somewhere else in the container," Mr. Hodges warned. "Testing all ground beef destroys all of the product. In short, the only way to test beef products and be absolutely certain that there’s no O157 in ground beef is to test it all."

Although testing is important, it is only one part of a total food-safety system. "We have to take a total food-safety system approach from the live animal through the slaughter process through various microbial reduction intervention technologies — testing to verify the adequacy of those manufacturing processes — and maintain the integrity of the product through the cold-chain distribution system and finally to the consumer where proper cooking is the final hurdle to beef safety," Mr. Hodges said.

"Thorough cooking to 160°F is the best tool we have to assure the safety of the product," he added. "Instant-read thermometers are essential tools to verify the product is cooked properly and they must be used at foodservice as well as in the home."

Finally, sampling and microbiological testing are useful to establish baseline data, screen raw products and verify control. However, it’s not often practical to sample and test a sufficient number of samples to obtain meaningful information relative to a specific lot or batch. "It must be recognized that no feasible sampling plan can ensure absence of a pathogen," Mr. Hodges said.

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