Two of the victims are from Minnesota, with the others being from New York, California and Arkansas. Health officials are confident that the deaths are due to contaminated lettuce, but have not been able to pinpoint precisely the source of the contamination.
Officials say that the E. coli making people sick have been traced to the romaine lettuce produced from the Yuma growing region in Arizona.
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.
"Any contaminated product from the Yuma growing region has already worked its way through the food supply and is no longer available for consumption".
This is the largest outbreak of its kind since a deadly E.coli outbreak in 2006 that was linked to spinach, CNN reported.
But in early spring, Yuma is the main source for lettuce sold across much of the U.S.
While washing produce may remove pesticide residue, dirt and debris, it's not effective at eliminating E. coli, which can even get into the interior of lettuce. The romaine lettuce you see in the stores right now is safe to consume.
Because majority of the illnesses came from prepackaged vegetables that have been passed on from suppliers to distributors to processing facilities where they were chopped and bagged, finding out where they were grown is far more cumbersome.
Symptoms vary, but it often include stomach cramps, bloody diarrhea, and vomiting.
They usually appear within three or four days of consuming the bacteria. Most people recover within a few weeks, but some suffer permanent damage or die. More severe cases included kidney failure and death.
Most E. coli bacteria are not harmful, but some produce toxins that can cause severe illness.
The outbreak hasn't only affected people who have eaten the lettuce, but also in some cases people they have come into contact with.