Three people who ate deli sandwiches from a restaurant in Canada’s largest cancer-care center have been infected with Listeria.

Toronto Public Health (TPH) is investigating the cases in people who ate at Druxy’s in the Princess Margaret Cancer Centre, the country’s largest cancer care center. TPH is asking anyone who ate deli meats at the restaurant between Jan. 1 and March 12 to watch for signs and symptoms of Listeria infection and seek medical attention if they have any.

“All the patients were quite ill,” Dr. Vinita Dubey, TPH associate medical officer of health, told the Toronto Sun.

Listeria infection can make anyone sick, but it presents a greater danger to adults over 60, pregnant women, young children and people with weakened immune systems, which makes it a particular concern to cancer patients.

Common symptoms include fever, diarrhea, vomiting, nausea and cramps. Severe symptoms include headache, stiff neck, confusion, loss of balance and convulsions. The symptoms can develop suddenly in people who have weak immune systems because of medical treatment or illness.

Symptoms usually occur within three weeks of eating foods contaminated with Listeria, but it can take up to 70 days in some people. There is no vaccine to prevent the Listeria infection, but it can be treated with antibiotics. Healthy people may only experience mild symptoms and usually recover completely. Individuals without symptoms do not need to be tested or treated.

Listeria infection is a serious but rare illness caused by eating food contaminated with the bacterium Listeria monocytogenes. Common foods contaminated with the bacteria include deli meats and unpasteurized, raw dairy products.

Healthcare providers frequently overlook Listeria as a possible cause of illness because of its unusual growth capabilities. Laboratories sometimes have a difficult time culturing Listeria, and when they can, it can be confused with other, less harmful contaminants and disregarded.

TPH staff have completed an extensive risk assessment, collected samples of the surfaces and food for testing and ordered a thorough cleaning of the restaurant and equipment inside the Princess Margaret Druxy’s. The restaurant is closed at this time to prevent further risk to the public. Public health officials have issued an alert to Toronto hospitals, long-term care facilities and doctors’ offices to make sure they are aware of the illnesses and possibility of additional patients with Listeria infections.

About 2,500 illnesses and 500 deaths are attributed to listeriosis in the United States each year. Toronto generally has about 17 cases a year.

Food-processing environment is vulnerable to Listeria monocytogenes from sources including infected employees, contaminated raw materials and failure to properly clean equipment and drains. Control is complicated by the bacterium’s ability to survive and grow under conditions not generally tolerated by similar organisms — it can survive at temperatures from below freezing to body temperature and grows best at the 0 degrees F to 50 degrees F range, which includes the temperature range used for freezing and refrigeration.

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