Recent foodborne illness outbreaks have pushed pathogen testing into the headlines, with national restaurant chains and local eateries touting negative test results as positive news.
Executives for the Denver-based fast-food burrito chain Chipotle Mexican Grill are relying on pathogen testing of fresh produce as part of their response to six foodborne outbreaks in the last six months of 2015.
The owner of a local bar and grill in Estill County Kentucky — the Eagles Roost — voluntarily closed down and sanitized his operation when several customers developed infections from Salmonella after eating there. Health officials collected environmental samples after the cleaning and gave the restaurant a score of 99 out of 100 when they returned negative results.
The cause of the Kentucky outbreak remains unknown, according to state officials.
But last week when some of the country’s top food safety experts discussed what pathogen testing can and cannot do, there was one thing they said is absolutely known.
“You can’t test your way to food safety” was the first, second and third verse during a webinar sponsored by the Produce Marketing Association (PMA).
Bob Whitaker, biologist and chief science officer at PMA, moderated the session with Trevor Suslow, extension researcher based at the University of California-Davis, and Jim Gorny, PMA’s vice president for food safety and technology and former senior advisor for produce safety at the U.S. Food and Drug Administration’s Center for Food Safety and Applied Nutrition.
The three scientists agreed that pathogen testing can be a valuable part of a food safety program, but cautioned it can also give a false sense of security to consumers and corporate executives.
Gorny invoked the words of astrophysicist and author Carl Sagan to explain why a fist full of negatives isn’t necessarily positive proof of anything.
“As Carl Sagan said, absence of evidence is not evidence of absence,” Gorny said.
Gorny used a simple equation to illustrate how easy it is to receive a false negative. His example used red and white balls, but it could just as easily have been tomatoes headed for Chipotle’s kitchens.
If you have 200 tomatoes and one of them is contaminated, you only have an 86 percent chance of finding the bad one if you pull out a sample of 30 tomatoes. When produce is tested, a much smaller sample is generally collected and tested. Making it even less likely that pathogens will be detected.
Suslow, who specializes in post-harvest food safety with fresh produce, stressed the importance of what kind of tests are being used and whether they allow for long enough enrichment periods. Suslow and Gorny both said the quicker the test, the less likely it is to reveal pathogens that are actually present.
In the produce industry, with short shelf life having such a strong impact on bottom lines, rapid pathogen testing is popular, but bordering on pointless, according to the experts.
Suslow said customer demands — often with no basis in science — are driving much of the pathogen testing that has been introduced in the past couple of years.
“To be honest it’s being used as a marketing advantage,” Suslow said.
However, all three scientists agreed that testing should be part of any good food safety plan. Environmental testing to ensure cleaning and sanitizing programs are working is an effective and proactive way use pathogen tests, Gorny said.
Gorny recommended waiting a couple of hours into a new shift before testing equipment, food contact surfaces and non-food contact surfaces. Suslow agreed, saying that cleaning products could skew test results. He suggested using a neutralizing agent when samples are collected.
Whitaker also promoted validation and verification testing as a proactive approach to food safety. He said pathogen testing as a preventive control is helpful, but not a guarantee.© Food Safety News