Fifty-eight people have been hospitalised and 102 are infected with E.Coli after eating lettuce.
Twenty-three US states have been affected by the outbreak, which started at a plant in Salinas, California.
The Centers for Disease Control has issued a recall and advised consumers not to eat any romaine lettuce grown in the region.
“If romaine lettuce does not have labelling information for its growing area or the source cannot be confirmed, consumers should not eat or use the romaine,” said Frank Yiannas, deputy commissioner for food policy and response at the US Food and Drug Administration.
“Restaurants and retailers should not serve or sell romaine lettuce if they cannot confirm it is from outside Salinas.”
Most people who swallow this strain experience possible bloody diarrhoea, severe stomach cramps and vomiting, the CDC says.
Recovery usually takes about a week, but the CDC says the strain can lead to longer and more severe illness.