Stories from the Field

Sample of Gouda Cheese that Caused an E. Coli Outbreak in October 2010
Chasing the Cheese

Between October 16 and October 27 last year, 38 people became ill with bloody diarrhea and abdominal cramps. Fifteen were hospitalized and one suffered kidney failure.


Although the ill were spread out across five states, public health laboratory testing—with results reported to PulseNet, a national food safety database—enabled health authorities to quickly connect the dots: all of the patients were infected with an identical, rare strain of E. coli O157:H7. In other words, these were not random cases of illness occurring hundreds of miles apart; they were all part of a common foodborne outbreak.

Once this determination was made, the race was on. Health authorities knew they needed to quickly identify the source of the outbreak before more people fell ill.

Based on patient surveys, epidemiologists in the five states—Arizona, California, Colorado, New Mexico and Nevada—determined that all of the patients had eaten free cheese samples during a Costco “cheese road show.” But which cheese was the tainted product?

Roumen Penev, PhD, and his fellow microbiologists at the Arizona Bureau of State Laboratory Services were the first scientists to isolate E. coli O157:H7 in a package of raw milk Gouda from a patient’s home.  

Even before the organism was characterized and shown to match the outbreak strain of E. coli O157:H7, Costco removed the product from its shelves and issued a consumer advisory, and the cheese manufacturer issued a voluntary product recall. On November 8, the Arizona laboratory confirmed that the E. coli isolated from the Gouda matched the DNA ‘fingerprint’ of the outbreak strain isolated from patient stool specimens. 

But the story does not end here.

The US Food and Drug Administration (FDA) cannot take regulatory actions based on findings from an opened food product, since contamination may have occurred after the package was unsealed.

New Mexico epidemiologists wanted to provide the agency with clear cut evidence. They enlisted officials from the state department of agriculture to procure unopened, suspect cheese products from a local Costco. These, in turn, were tested by Paul Torres, MS, and colleagues in the environmental microbiology section of the New Mexico public health laboratory.

“They brought us the samples late on a Friday,” said Torres. “We started testing on Saturday.” Not only did the scientists isolate E. coli O157:H7, but, said Torres, “The samples also had large numbers of fecal coliforms, with one sample as high as 11,000 fecal coliforms per gram.” The finding, he said, “is pretty scary, because cheese is something you’d likely eat uncooked.” 

The New Mexico scientists knew by November 10 that they had isolated the culpable bug.

Quick, coordinated action on the part of state and federal agencies undoubtedly spared more people from severe E. coli O157:H7 illness.

Moreover, the uptick in cheese testing in the affected states turned up additional tainted products. A gorgonzola tested by the Colorado Laboratory Services Division was found to have a different strain of E. coli O157:H7, and cheese samples tested by the California Department of Food and Agriculture were found to have Listeria monocytogenes as well as E. coli O157:H7. All tainted products were voluntarily removed from the market—and undistributed products seized by the FDA—before any clusters of patient illness were reported. An incredible food safety success.