This undated photo shows romaine lettuce shot in the Houston Chronicle newspaper studio.
What is still not known is exactly where the lettuce was tainted by the E. coli.
Of 158 patients interviewed by state and local health officials, all but 18 reported eating romaine lettuce in the week before their illness started. Since lettuce has a 21-day shelf life, it is unlikely that any romaine lettuce from the area remains in restaurants, stores or people's homes, the CDC said.
Since mid-May, "four more deaths were reported, bringing the total to five deaths from Arkansas (1), California (1), Minnesota (2), and NY (1)", the CDC said in a statement.
- Four more deaths have been reported in the multi-state E. coli outbreak linked to romaine lettuce from Yuma, Arizona, the CDC confirmed in a June 1 update. Of 187 people with information available, 89 (48 percent) have been hospitalized, including 26 people who developed hemolytic uremic syndrome, a type of kidney failure.
Previously one death had been reported, in California.
Officials said that first illness began sometime between March 13 and May 12. Health officials said there are now 197 cases across 35 states.
Most new cases involve people who became sick two or three weeks ago, when the tainted lettuce was still available for sale.
The CDC has not pinpointed the exact source of the outbreak, but the lettuce appears to have been contaminated with Shiga toxin-producing E. coli O157:H7, a particularly risky strain of the bacteria. People who get sick from toxin-producing E. coli come down with symptoms about three to four days after swallowing the germ, with many suffering bloody diarrhea, severe stomach cramps and vomiting.
Most people recover within a week, but some illnesses can last longer and be more severe.