Three people have died following a listeria outbreak at a family-owned burger restaurant in Tacoma, Washington. On Aug. 18, the Washington State Department of Health released a report confirming that listeria bacteria were found in all milkshake flavors sold at a Frugals burger restaurant in Tacoma, about one hour from Seattle. The department reported that the bacteria led to six hospitalizations and three deaths. Those hospitalized were between the ages of 40 and 79 . “Investigators found Listeria in the ice cream machines, which were not cleaned correctly,” the department said. “No other Frugals restaurants are believed to be affected.” Although Frugals Tacoma stopped using its ice cream machines on Aug. 8, the department pointed out that listeria can continue to afflict people for up to 70 days. The Washington State Department of Health also encouraged people who are pregnant, 65 or older and those with weakened immune systems to contact their health care provider if they drank a milkshake at Frugals Tacoma between May 29 and Aug. 7 and are having symptoms. According to the Centers for Disease Control and Prevention , listeria infection, or listeriosis, occurs after eating food contaminated with a bacterium called Listeria monocytogenes. Some of the symptoms are fever, muscle aches, fatigue, headache, stiff neck, confusion, loss of balance, seizures, diarrhea and vomiting, the center said. The same strain of listeria was detected in all six people who were hospitalized between Feb. 27 and July 22, the Washington State Department of Health said. “All six people had conditions that made their immune systems less able to fight disease,” the department reported. Frugals Tacoma posted a statement about the outbreak on its Instagram page Aug. 19. “Last week, Frugals was notified by the Pierce County Health Department (PCHD) of an investigation into a possible listeria outbreak at our Tacoma Frugals locations. Since that time, we have been working with PCHD to identify and contain the source of listeria after a test on a milkshake machine in our Tacoma store tested positive for the bacteria,” the statement began. Frugals Tacoma said the chain was “deeply saddened” to learn that six people were treated at a hospital and three died after contracting the bacteria. “We are heartbroken and deeply regret any harm our actions could have caused,” the statement said. The burger chain said it is following the PCHD’s recommendations and sent its milkshake equipment to an independent facility to be cleaned and sanitized before being tested again for the bacteria. Frugals also said it sent testing samples from milkshake machines at its other locations and has shut down all milkshake machines as the chain awaits the results. “As a family-owned business for over 30 years, the trust of our customers is paramount,” Frugals said. “We will continue to fully cooperate with this investigation, and we are committed to making any changes deemed necessary to maintain our high standard of operations and prevent this from happening again.” TODAY.com reached out to the burger restaurant’s headquarters for additional comment but did not immediately hear back as of Aug. 21.