BOSTON (AP) – Investigators probing the source of a listeria outbreak said Thursday they found the strain of the bacteria that killed three people in bottles of milk at a Shrewsbury dairy processing plant and on the floor near the homogenizer, but they have not yet determined exactly where the milk was contaminated.
“We know that there’s a problem in that plant and we have connected the patients to the products at the plant, now it would be nice to know exactly how that happened, but that is part of the ongoing investigation,” said Dr. Alfred DeMaria, state director of communicable disease control.
Three elderly men have died since June after drinking bacteria-contaminated milk from the Whittier Farms plant in Shrewsbury, about 35 miles west of Boston. The same strain of listeria sickened a pregnant woman, who then miscarried. A second woman also was sickened after drinking milk from the plant.
No new cases have been identified and officials at the state Public Health Department say the public health risk is low.
“It’s a good sign that we haven’t had any potential cases in the past several weeks, and we’ll continue heightened surveillance for the next several weeks,” DeMaria said.
The deadly strain was found in seven bottles and the floor of the plant, which has been closed since December. Different listeria strains were found inside four other bottles of milk and at three different areas inside the plant – in a drain, in a bottle washer and in an empty unwashed bottle.
More than 100 samples were taken.
It remains unclear how the milk was contaminated, but one theory is that processing equipment may have unintentionally been contaminated during cleaning activities, allowing the bacteria to enter the milk, state officials said.
Listeria was found mostly in flavored milk, suggesting that the sugar content of the flavoring syrups provided an environment that enhanced bacterial growth, officials said.
The processing plant, which distributes milk under various brand names to homes and stores across central Massachusetts and also operates a 500-acre farm in the town of Sutton, would remain closed during the investigation and until the bacteria is eradicated, officials said.
One of the farm’s owners has said they were selling the milk produced by their herd of 350 Holsteins to other processors. A call to Whittier Farms on Thursday was not immediately returned.
DeMaria said officials would next examine the plant’s processing procedures for more clues of how the milk was contaminated.
When the investigation ends, it will be up to Whittier’s owners to decontaminate the plant. The state will inspect it to ensure the milk being processed there is safe.
“We will not allow milk to be sold from this plant until we have assurance that this won’t reoccur,” said Suzanne Condon, director of the Bureau of Environmental Affairs.
Listeria is extremely rare in pasteurized milk because the process is supposed to kill the germ. Health officials have said they found nothing wrong with the pasteurization process, but on Thursday said the process would be further examined.
Listeria is more often found in raw foods, including uncooked meat and vegetables, and processed foods, including cheeses and cold cuts.
The bacteria can cause listeriosis in humans, which can be fatal, especially in those with weakened immune systems.
AP-ES-01-17-08 1518EST
Send questions/comments to the editors.
