Published: 2018-06-02 03:12:44 BdST
Twenty-five more people have taken ill since the last update from the agency on May 16, with 197 patients from 35 states now affected, the CDC said.
The patients who died were from Arkansas, California, Minnesota and New York.
Some affected people did not report eating romaine lettuce, but had contact with those who fell ill after consuming the popular salad plant, the CDC said.
Most new cases involve people who became sick two or three weeks ago, when the tainted lettuce was still available for sale.
The US Food And Drug Administration has said the harvest season for romaine lettuce is over.
The reported strain of E coli, which produces poisonous substances known as Shiga toxins, can cause severe stomach cramps, bloody diarrhoea and vomiting.