SALT LAKE CITY — Officials with the Salt Lake Valley Health Department have tracked the source of a three-year outbreak of salmonella to an unauthorized food producer in Salt Lake City.

A man referred to as "Mr. Cheese" was apparently producing queso fresco in his home using raw milk.

Since 2009, health department officials noticed an increase in the number of salmonella Newport cases and believe as many as 2,000 Utahns in six counties — Salt Lake, Davis, Weber, Morgan, Tooele and Utah — may have been affected, said Dr. Royal DeLegge, director of Salt Lake Valley Health Department's Environmental Health Division.

He said the illness often goes unreported because it leads to nausea, vomiting and diarrhea and is mistaken for a stomach virus.

"The general assumption is that the actual number of cases is, on average, 30 times as large as those you actually know about," DeLegge said, explaining that there were 80 known cases, but possibly thousands that are unknown. "That's why it's such an issue of public health."

Experts tracked the outbreak through 2011 and, in July — following an investigation and a number of tests — were able to find a common source of the bacteria at an undisclosed restaurant/deli-type facility in Salt Lake City. Health officials, with the help of an investigator from the Salt Lake County District Attorney's office, were then able to identify a man they believe was producing the cheese.

"We put together a photo lineup and took it to the operator of the facility," DeLegge said. "He identified the individual as Mr. Cheese, who was a supplier to him."

Investigators from the Utah Department of Agriculture and Food went to the man's home in Salt Lake City and found the cheese-making operation. The man explained the process he used and the source of the raw milk he was using — a dairy located outside of Heber.

"Raw milk in the state of Utah can only be sold directly from the dairy to an individual," DeLegge said. "It cannot be transmitted by second or third parties."

He said raw milk is inherently more dangerous than pasteurized milk products. Tom Trevino, with the health department's Bureau of Food Protection, added that dairies must have a permit or license to sell the raw milk to individuals and the dairy in Heber had neither.

DeLegge said a notice of violation has been filed regarding the facility selling the product in Salt Lake City and a cease and desist order has been sent.

Though the illness typically lasts two to three days, Trevino said it sends as many as one-quarter to one-third of those afflicted to the hospital. DeLegge said the severity of salmonella can vary from individual to individual, but can be potentially life-threatening to those in "sensitive populations" such as the very old or very young or those with compromised immune systems.

"What we're asking people to do is exercise common sense when purchasing food products," DeLegge said. "We have food products being distributed out of trunks in parking lots, door-to-door, people are being solicited all the time for products being produced in someone's home. We would advise that that's probably not a good idea."

He also suggested that individuals should check that products they purchase in stores are properly labeled.

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