Outbreak investigators are warning the public that romaine lettuce linked to an outbreak of E. coli O157 in Canada is a potentially deadly strain having already hospitalized half of the victims. Three provincial health departments are reporting outbreak cases, with 21 sick people confirmed so far. Ten of the victims have had symptoms so severe that they required hospitalization. The Public Health Agency of Canada posted an outbreak notice Monday. The agency did not report whether the outbreak is ongoing. “Individuals became sick in November 2017. Ten individuals were hospitalized. No deaths have been reported. Individuals who became ill are between the ages of 5 and 72 years of age” the federal health agency reported. “Many individuals who became sick reported eating romaine lettuce before their illnesses occurred. The Canadian Food Inspection Agency (CFIA) is working with public health officials to determine the source of the romaine lettuce that ill individuals were exposed to.” Health officials did not report the onset dates for the 21 sick people, so it is not known if any illnesses began in late November, which would suggest some of the implicated romaine lettuce could still be in the stream of commerce. Tuesday a spokeswoman for the federal health agency referred Food Safety News to the outbreak notice, stating it had all of the currently available information. The notice does not indicate when public health officials became aware of the November outbreak or why it was not revealed to the public until Dec. 11. Also, the health agency notice does not provide any information on the brands of lettuce or retailers that sold it. Neither the health agency nor the Canadian Food Inspection Agency has posted any information about recalls of any romaine lettuce or other foods about the outbreak. “The outbreak investigation is ongoing, and this public health notice will be updated on a regular basis as the investigation evolves,” according to the notice. Currently, there are 21 cases of E. coli O157 illness under investigation in three provinces: Quebec with 3 cases, New Brunswick with 5 cases, and Newfoundland and Labrador with 13 cases. Advice to consumers Although anyone can get an E. coli infection, pregnant women, those with weakened immune systems, young children and older adults are most at risk for developing severe complications. Anyone who has eaten romaine lettuce and developed symptoms of E. coli infection should immediately seek medical attention. Symptoms can include nausea, vomiting, headache, mild fever, severe stomach cramps, and watery or bloody diarrhea. The onset of symptoms can range from 1 to 10 days after exposure. “Some do not get sick at all, though they can still spread the infection to others. Others may feel as though they have a bad case of upset stomach. In some cases, individuals become seriously ill and must be hospitalized,” according to the health agency notice. “People who develop complications may need further treatment, like dialysis for kidney failure.” (To sign up for a free subscription to Food Safety News, click here.)