Ten Minnesotans have been sickened and three hospitalized after eating romaine lettuce that has been linked to multiple E. coli infections across the country.

The 10 are Minnesota’s first cases in a national outbreak of toxic E. coli O157 that has sickened more than 121 people and caused one death.

“This particular strain does appear to be more severe than what we might normally see,” said Amy Saupe, a foodborne disease epidemiologist for the Minnesota Department of Health, which announced the illnesses Tuesday.

Cases have continued to emerge nationally even after the first reports appeared in New Jersey in early April.

The infections have been traced largely to lettuce grown in the Yuma region of Arizona. While lettuce from the region should have been removed from grocery stores by now, state health officials warned consumers to check their refrigerators.

“Do not eat, buy, or sell romaine lettuce unless you can confirm it is not from the Yuma growing region,” said Kirk Smith, a manager of the health department’s foodborne diseases unit.

The Minnesotans suffered their illnesses between April 20 and May 2, and reported eating lettuce from stores, restaurants or residential facilities. Most were women. The cases occurred statewide.

Two of the stricken individuals suffered hemolytic-uremic syndrome, a potentially fatal complication that can cause kidney failure, due to their infections. One remains hospitalized.

Many forms of E. coli are not harmful — and play important roles in human digestion — but the O157 strain produces a Shiga toxin that causes illness. Classic symptoms include stomach cramps and diarrhea, but with only a low fever.

Roughly 135 such infections are reported in Minnesota each year. The romaine E. coli outbreak is the largest in the U.S. since a 2006 outbreak tied to spinach that sickened at least 199 people in 26 states.

Federal and state disease investigators are continuing to search for the precise point in the food distribution chain where the lettuce was exposed to E. coli O157. The challenge in this instance is that lettuce comes from numerous growers in the region and can be commingled with other lettuce or food products.

The bacteria can survive on lettuce even after weeks in cold storage, Saupe said. “It might not grow very quickly and multiply, but whatever E. coli is on the romaine already won’t be killed by refrigerator temperatures.”