Three people have died and three others have been hospitalized after drinking milkshakes contaminated with Listeria bacteria from a restaurant in Tacoma, Washington, health officials say.

Investigators found the outbreak was linked to ice cream machines that were not cleaned properly at a Frugals restaurant in Tacoma, according to a release from the Washington State Department of Health. Listeria can affect people up to 70 days after consumption and the machines were used through August 7, the release said.

CNN has reached out to Frugals but has not immediately heard back.

The six individuals were hospitalized between February 27 and July 22 and genetic fingerprinting from the bacteria inside the milkshakes showed it was the same strain of Listeria that triggered the hospitalizations, the health department says.

Two of the three who survived said they had a milkshake from the same Frugals in Tacoma before getting sick.

Symptoms of Listeria infection include fever and muscle aches, and sometimes diarrhea or other gastrointestinal problems. Other symptoms are headache, confusion and convulsions.

The health department said no other Frugals restaurants are believed to be affected by the outbreak.

Anyone who ate at the Tacoma restaurant between May 29 and August 7 and is showing symptoms of Listeria is urged to contact a doctor, the agency cautioned.

According to the Centers for Disease Control and Prevention, the Listeria monocytogene bacteria causes an estimated 1,600 cases of listeriosis in the United States annually. Around 260 people die from the disease each year.

It typically affects older adults, pregnant women, infants and adults with compromised immune systems.

Pregnant women are approximately 10 times more likely to get listeriosis, and pregnant Hispanic women are 24 times more likely, according to the CDC.