False Negatives for Common Pathogens Frequent in Food Laboratory Assessment

The accuracy of food microbiology laboratory testing for common pathogens “remains problematic,” according to a review of proficiency test results over a period of 14 years. The average percentage of false negative results in the review of almost 40,000 results was more than 5 percent for several common pathogens, researchers reported at the American Society for Microbiology meeting, May 18-21, in Denver.

“Our objective in conducting this study was to assess whether laboratories have improved their ability to detect or rule out contamination over a 14-year period,” said Christopher Snabes, BS, MS, CFS, a food technical specialist at the American Proficiency Institute and the first author of the study. The Institute, in Traverse City, Mich., has offered food microbiology and food chemistry proficiency testing since 1999.

The researchers examined the false positive and false negative rates of participating laboratories for four common pathogens. On average, the false negative rate for Escherichia coli O157:H7 was 6.6 percent, for Salmonella spp. 4.9 percent, for Listeria monocytogenes 5.7 percent, and for Campylobacter spp. 9.1 percent. The average false positive rates were 2.5 percent for E. coli O157:H7, 3.9 percent for Salmonella spp., 2.5 percent for L. monocytogenes, and 3.6 percent for Campylobacter spp.

False negative rates for certain pathogens in individual years were as high as 19.8 percent, Snabes said in an email to Food Quality.

“We noted that the cumulative performance of proficiency testing rates decreased slightly from 2011 to 2012 for false negatives,” he said. “Similarly, there was a slight decline in false positives for some pathogens over the last two cumulative years. Improvement in the ability of food laboratories to detect pathogens is critical, but it is too early to say if this is a trend that will continue.”

Snabes noted that proficiency testing, which is mandated for clinical laboratories, is still a voluntary quality assessment tool for food microbiology labs. Similar requirements for food laboratories may be mandated when final rules for the Food Safety Modernization Act are promulgated.

“Laboratories remain a critical partner in the food safety system,” he said. “Proficiency testing is there to assist them in ensuring success.”

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