Three people have died, and three others are in hospital after drinking milkshakes contaminated with listeria bacteria in the US state of Washington.

Investigators found the bacteria in the ice cream machines at Furgals, a popular burger and milkshakes restaurant in Tacoma. The restaurant said in a statement it was “deeply saddened” by the news.

Listeria can affect people up to 70 days after consuming contaminated food. Health officials say the ice cream machines at the Tacoma restaurant were not cleaned correctly resulting in a foodborne listeriosis outbreak.

Washington State Department of Health said six people were sent to the hospital between 27th February and July 22nd. These people had weakened immune systems and are between the ages of 40 and 79. The business has stopped selling milkshakes at the Tacoma location and has sent its equipment to an independent facility for cleaning and re-testing.

The Centers for Disease Control and Prevention estimates about one thousand 600 Americans are infected by listeria every year, and some 260 Deaths.