There is typically a lag between the time when someone falls ill and the CDC is alerted.
On Friday the Centers for Disease Control and Prevention said 197 people from 35 states have been sickened in the outbreak since March 13.
Two of the victims were from Minnesota, with the other three from Arkansas, California and NY.
The recent E. coli outbreak is the most severe to hit the US since 2006, when three people died in an outbreak linked to uncooked spinach.
The latest batch of illnesses are believed to be linked to romaine lettuce grown in the Yuma, Arizona region. On Friday, health officials said they have learned of four more - another in California as well as one each in Arkansas, Minnesota and NY.
"Most of the newly reported cases are people who became sick two to three weeks ago, still within the window when contaminated romaine was available for sale", said the CDC statement. A total of 26 people have developed a type of kidney failure called hemolytic uremic syndrome.
Unlike spinach, which is often cooked, romaine - and lettuce in general - is more common as a culprit in E.coli outbreaks because it's eaten raw.
"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".
Officials urge anyone who thinks they may be ill with an E. coli infection to see their doctor. The growing season in Yuma ended April 16.
Symptoms, which begin about three to four days after consuming the bacteria, can include watery or bloody diarrhea, fever, abdominal cramps, nausea and vomiting, according to the CDC.
Most people recover within a week, but some illnesses can last longer and be more severe.