E. coli O157:H7 is the same strain that killed seven people in Walkerton, Ont. in 2000.
The source of the infectious bacteria that multiplies quickly remains unclear.
Public health is investigating to determine where the affected individuals in Fredericton ate, what they ate, and whether the cases might be connected, said Dr. Denis Allard, the province's acting chief medical officer of health, in a statement.
"Pending lab results could determine if the bacteria share the same DNA pattern, suggesting a common source," Allard said.
It could be next week before those results are available, he added, declining any further comment.
This particular strain of E. coli secretes a powerful toxin that can destroy red blood cells leading to severe illness, high blood pressure and kidney damage.
Allard says three of the Fredericton cases were hospitalized. Two have been treated and released.
The main symptom for this strain of E. coli is bloody diarrhea, but it can also cause vomiting and stomach cramps. Unlike other illnesses, there is no fever.
Those most at risk of developing serious complications include pregnant women, young children, seniors and people with a weakened immune system, such as those on chemotherapy.
Follows Miramichi outbreak
The confirmed cases come on the heels of an outbreak in Miramichi in April.
At least 13 people were infected with the potentially deadly strain and another 11 people may have also been infected by the same strain, officials had said.
Romaine lettuce was recently determined to be the likely source of that outbreak.
The Department of Health conducted a case control study that examined 55 people, including 18 individuals who were sick and 37 people who were not sick.
All of those in the study who were sick with E. coli appear to have consumed romaine lettuce that was used in salads, as an ingredient in wraps, or as a garnish for hamburgers, Dr. Eilish Cleary, the chief medical officer of health, said at the time.
The study focused on those who ate at Jungle Jim's in Miramichi between April 23 and 26.
The provincial government announced new food safety regulations in May.
As of July 1, restaurants must ensure one person on every shift is certified in safe food handling.
Steps to avoid the bacteria include:
- regular hand washing, especially after using the washroom and when preparing food
- washing fruits and vegetables
- properly cooking meatusing warm soapy water or a chlorine-based or other approved sanitizers to clean knives, cutting boards, utensils, and any counters or surfaces that have come in contact with food, especially meat and fish
During the Walkerton outbreak, the water supply had been contaminated.