In an update Friday, health officials said 25 more cases have been added, raising the total number of illnesses to 197 in 35 states.
Still, the CDC warns that iIllnesses that occurred after May 6, 2018 might not yet be reported due to the time it takes between when a person becomes ill and when the illness is reported. The new CDC report announces four more deaths - one in Arkansas, two in Minnesota and one in NY.
Two of the victims were from Minnesota, with the other three from Arkansas, California and NY. On Friday, health officials said they had learned of four more - one in Arkansas, one in NY, and two in Minnesota.
Officials said that first illness began sometime between March 13 and May 12.
Numerous new cases were people who became ill two to three weeks ago, when contaminated lettuce was still being sold. A total of 26 people have developed a type of kidney failure called hemolytic uremic syndrome.
"Some people who became sick did not report eating romaine lettuce, but had close contact with someone else who got sick from eating romaine lettuce".
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 unsafe strain of the bacteria.
While most people recover within a week, some illnesses can last longer and be more severe, the CDC cautioned.
This is the largest outbreak of its kind since a deadly E.coli outbreak in 2006 that was linked to spinach, CNN reported.