For the third time since 2005, researchers have parsed data from an E. coli O157: H7 outbreak traced to raw milk gouda cheese. For the third time, they have concluded the “60-day rule” isn’t long enough to ensure dangerous bacteria in unpasteurized gouda have died.
This time around the scientists did more than publish the information, though. They are telling the government that the 1950s-vintage 60-day rule needs to be revisited because it is obsolete when viewed under 21st Century microscopes.
The antiquated rule “assumed that any pathogens present would die off over time in an environment of low pH, low water activity, and high salt and the presence of competitive microflora in the cheese,” according to the most recent research report.
“However, these assumptions were made before E. coli O157: H7, Listeria monocytogenes, and Salmonella were recognized as common foodborne pathogens and before evidence had accumulated regarding the ability of these pathogens to tolerate these conditions.
“Hard and semihard cheeses have long been considered a lower risk to public health than soft and semisoft cheeses, but further evaluation is warranted for Gouda cheese in particular, given recurrent outbreaks associated with this semihard variety.”
Two of the outbreaks referenced in the research published in the February edition of the Journal of Food Protection occurred in Canada, in 2002-03 and 2013. The first sickened at least 13 people. The 2013 outbreak sickened 29 people, killing one.
The third outbreak was in 2010, with 41 people across the Southwestern United States confirmed with E. coli O157: H7 infections.
All three outbreaks were traced to gouda cheese made with unpasteurized, raw milk.
Outbreak investigations revealed live E. coli O157: H7 present in unopened gouda samples that were well past the 60-day aging requirement, according to the most recent research by scientists from numerous federal and provincial public health agencies in Canada.
Raw milk gouda tested during the investigation of the 2013 outbreak showed live E. coli present 306 days after it was produced.
“This finding is consistent with those from other outbreaks and microbiological studies of artificially contaminated cheeses that have revealed that pathogenic bacteria, including E. coli O157: H7, can survive in various varieties of cheese through production and the subsequent aging and storage periods at levels sufficient to cause human illness,” the Canadian research team reports in this month’s edition of the Journal.
The scientists also looked at the manufacturing practices at the cheese production facilities and found they were operating within the applicable laws and regulations.
“… no major deviations in cheese production and subsequent handling were noted in the outbreak presented herein or in the E. coli O157: H7 infection outbreak attributed to raw milk Gouda cheese in Canada in 2002. The implicated cheeses were produced in accordance with regulated microbiological and aging requirements.”
Consequently, the scientists report, if E. coli is present in the raw milk used to make the cheese, it does not die during the minimum 60-day aging period. Instead, the potentially deadly pathogen can survive for five times that long in large enough numbers to cause infections in people who eat it.
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