The outbreak appeared to be over, more than three months after the first illnesses were recorded, the Centers for Disease Control and Prevention said.
In April, the outbreak was traced back to lettuce grown in the Yuma region of Arizona, later resulting in a halt in production of all lettuce from the region.
The diseases in 36 states were earlier found to romaine lettuce made in Yuma, Arizona, which gives a large portion of the romaine sold in the USA amid the winter.
"To date, CDC analysis of samples taken from canal water in the region has identified the presence of E. coli O157:H7 with the same genetic fingerprint as the outbreak strain", the FDA said in a June 28 update.
It was the largest E. coli flare-up in more than a decade.
FDA Commissioner Dr. Scott Gottlieb said the outbreak has ended but work needs to be done to determine how and why this strain of E. coli got into the canals in Yuma, and how that led to contamination of lettuce from multiple farms.
In total, 210 cases were reported from 36 states.
Bill Marler, a prominent food-safety lawyer who represents 105 patients sickened by the lettuce, said he was not surprised that the probable link was broad environmental contamination, such as by water, given the number of people sickened and the number of unnamed farms and fields implicated.
"It is encouraging that public health officials found the outbreak strain of E. coli bacteria in the area", Fred added.
The Food and Drug Administration is still trying to find out how the bacteria got into the water and the lettuce. The agency received confirmation of the final harvest of romaine from the Yuma region on May 2, and the vegetable has a 21-day shelf life. Ninety-six people were hospitalized, 27 developed kidney failure, and five died. "But it's troubling that other strains of this risky bacteria were found in environmental samples and that no specific farm was identified".
5 people died, one each in Arkansas, California, and NY. Other kinds of E. coli cause urinary tract infections, respiratory illness and pneumonia.