Illnesses have been reported from British Columbia (4), Saskatchewan (4), and Newfoundland and Labrador (4) and four people were hospitalized.
Onset dates range from November to December 2016.
Nine males and three females have been affected and the age range is from nine to 79 years old.
The Public Health Agency of Canada (PHAC) said the source has not yet been identified.
It said the risk was low but advised the public to follow safe food handling practices to avoid illness.
“Two of the most common ways to come into contact with E. coli are by improperly handling raw ground meat and by eating ground meat that is undercooked.
“Common sources of E. coli may also be contaminated raw fruits and vegetables, untreated water, unpasteurized milk and raw milk products, and unpasteurized apple juice or cider.”
The Canadian Food Inspection Agency (CFIA) is attempting to find the possible food source of the outbreak.
E. coli O121:H19 (15 isolates) was among the top three most commonly reported non-O157 serovars to the National Enteric Surveillance Program (NESP) in 2014.
Symptoms can appear within one to ten days after contact with the bacteria.
They usually clear up within five to ten days but some people can develop life-threatening symptoms, including kidney failure, seizures and stroke.
There is no real treatment for infection, other than monitoring illness and preventing dehydration through proper hydration and nutrition.
People infected with E. coli may not get sick but can still spread it to others.
E. coli O121 is one of the serogroups of verotoxigenic E. coli (VTEC). These are distinguished from other E. coli by production of one or more verotoxins.
These pathogens are also known as Shiga toxin producing E. coli (STEC) and enterohemorrhagic E. coli (EHEC).