Public health officials in the U.S. investigating an outbreak of listeria have found 16 samples of listeria bacteria at a milk processing plant.
The outbreak has resulted in the deaths of 3 elderly men who have died since June after drinking milk that was contaminated with the bacteria.
The same strain of listeria also sickened a pregnant woman, who then miscarried and a second woman also was sickened after drinking milk from the plant.
The dairy processing plant in Shrewsbury is 35 miles west of Boston in Massachusetts, and is owned by Whittier Farms.
While officials have yet to determine exactly how the milk was contaminated, one environmental swab, one skim milk sample and seven flavoured milk samples tested positive for the same strain of listeria that is now being blamed for the outbreak that sickened people.
The milk appears to have been contaminated during the production process and it is suspected that the processing equipment may have unintentionally been contaminated during cleaning.
Susanne Condon, director of bureau of environmental health says this is just one of the theories being examined.
As no new cases have been identified, health officials say the health risk to the public is low.
The processing plant distributes milk under various brand names to stores across central Massachusetts and also operates a 500-acre farm in the town of Sutton.
Officials say the plant has been closed since December and will remain so while investigations continue and the bacteria is eradicated.
Listeriosis is a type of food poisoning that can be particularly dangerous to the elderly, infants, pregnant women and people with chronic medical conditions; the symptoms include fever, headache, stiffness, nausea, abdominal pain and diarrhea.