The listeria germ that killed three people and sickened two others has been confirmed as originating on the production line of the Whittier Farm’s dairy in Shrewsbury, Massachusetts state disease investigators reported yesterday. This discovery provides the clearest evidence yet of how milk became contaminated with the deadly bacteria. Tests performed on the Whittier Farms plant found a strain of listeria on the floor identical to the type found in people who became ill last year after drinking the dairy’s milk. It is extremely rare to discover multiple listeria cases with identical genetic profiles. Generally, each infection generates from a different bacterium. In 19 other cases in Massachusetts last year, each infection was caused by a germ with a distinctive fingerprint. Likewise, there were no genetic matches among 99 cases in the previous five years.
Investigators discovered the germ near a key piece of equipment used after milk is pasteurized. “Finding it in the environment there closes the final loop,” said Dr. Alfred DeMaria, the state’s director of communicable disease control. “This was a totally unique strain.” That same strain was also identified in seven unopened containers of milk the state removed from a retail store next to the farm’s production facility and the germ was found in skim milk as well as coffee-, chocolate-, vanilla-, and strawberry-flavored milk. Review of the Whittier production line revealed unrelated strains of listeria in a drain, an unwashed bottle, and another piece of equipment. State investigators said they were unsure how listeria made its way inside the nationally recognized, family-owned dairy received the National Dairy Quality Regional Award for U.S. dairy producers, ranking Whittier Farms among the top dairy farms in the Northeast.
In recent visits, dairy industry representatives expressed surprise that listeria would be found in pasteurized milk since pasteurization is meant to kill germs. “Dairy products are among the safest products on the shelf, because they are pasteurized,” said Jenny Bourbeau, spokeswoman for the New England Dairy & Food Council, an industry organization. Perhaps workers carried it on their clothing or shoes from elsewhere on the farm, said Suzanne Condon, the top environmental health official at the state Department of Public Health. It is also possible that spray hoses used for cleaning might have spread the germ.
Investigators said it was unclear how the amount of listeria isolated at Whittier compared with other dairies. “The level of scrutiny that this particular facility is receiving now is far beyond what typically happens based on state and federal regulations,” Condon said.
Whittier Farms agreed to halt production in December, after authorities first linked it to the cases of listeria. Condon said the dairy will be allowed to resume production only after ensuring it can safely produce milk. “There are going to be things that will be required of this plant that go far beyond what would be typically required because of what we found,” Condon said.
Whittier makes milk products under the Whittier, Schultz, Balance Rock, Spring Brook, Model Dairy, and Maple brands.
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