Romaine lettuce has been determined to be the likely source of an E. coli outbreak in Miramichi in April.

The Department of Health released results of a case control study on Friday that examined 55 people, including 18 individuals who were sick and 37 people who were not sick.

The study looked at what the people ate to determine if there were any patterns.

Dr. Eilish Cleary, the chief medical officer of health, said all of those in the study who were sick with E. coli appear to have consumed romaine lettuce.

"The lettuce was used in salads, as an ingredient in wraps and hamburgers and as a garnish. These results indicate a strong likelihood that contaminated lettuce was served at the restaurant," Cleary said in a statement.

The Public Health Agency of Canada helped the province’s health department on the control study. The experts focused on the food items eaten by those who ate at Jungle Jim's in Miramichi between April 23 and 26.

The health department said information from the study will be used to bolster food safety measures.

The federal agency became aware that cases matching the E. coli strain involved in the Miramichi outbreak had also been identified in Quebec and California, according to the province’s statement.

The lettuce is no longer in the marketplace and the investigation has been closed, the department said.

E. coli 0157:H7 is the same strain that killed seven people in Walkerton, Ont., in 2000. It secretes a powerful toxin that can cause severe illness, high blood pressure and kidney damage.

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.