The strain of E. coli bacteria that contaminated romaine lettuce and was tied to the deaths of two Minnesotans and three others was found in a tainted irrigation canal in Arizona.

The outbreak appears to be over, more than three months after the first illnesses were recorded, according to the Centers for Disease Control and Prevention.

Samples of canal water in the Yuma area of Arizona were found to contain the same genetic strain of E. coli that caused the outbreak, Dr. Scott Gottlieb, commissioner of the federal Food and Drug Administration, said in a statement.

When eight inmates at an Alaska prison got sick, FDA investigators traced the illness back to whole-head romaine lettuce that was harvested from Harrison Farms in the Yuma area. Health officials said the lettuce that caused the national outbreak was linked to many farms in the region. Representatives of Harrison Farms could not be reached for comment.

Questions remain about how the bacteria ended up in the canal.

"More work needs to be done to determine just how and why this strain of E. coli O157:H7 could have gotten into this body of water and how that led to contamination of romaine lettuce from multiple farms," Gottlieb said.

Of the five people who died, two were women from Minnesota, and the others were from Arkansas, California and New York, according to the CDC. Those sickened were from 36 states.

It was the largest E. coli flare-up in more than a decade. More than 200 people got sick and about half of them had to be hospitalized.