ST. LOUIS — The U.S. Centers for Disease Control and Prevention has determined that romaine lettuce from a single farm is likely to blame for an E. coli outbreak in Missouri and nine other states.

Sixty people became sick in the outbreak that began in October and ended in November. No one died, but at least 30 were hospitalized and two developed severe kidney disease. Thirty-seven of the illnesses were in Missouri. Illinois had the second-most reported illnesses with nine. Other illnesses were reported in Arizona, Arkansas, Georgia, Indiana, Kansas, Kentucky, Minnesota and Nebraska.

St. Louis-based Schnuck Markets Inc. said Thursday that some of the contaminated lettuce was sold in the grocery store chain’s salad bars. However, the CDC said the lettuce was contaminated prior to distribution to Schnucks. The CDC did not name the supplier.

“What they’re telling us is they have tracked it back to one particular farm,” Schnucks spokeswoman Lori Willis said. Schnucks and CDC did not provide the location of the farm.

The CDC said the outbreak is over and consumers should no longer avoid eating lettuce from Schnucks or elsewhere.

E. coli are a group of bacteria that can cause diarrhea, urinary tract infections, respiratory illness and pneumonia. The illness is typically spread through consumption of contaminated food, unpasteurized milk, contaminated water or contact with the feces of infected people.

Young children and the elderly are most at risk of serious illness which can, in rare instances, be fatal. Health officials encouraged immediate medical attention for anyone with bloody or persistent diarrhea, severe stomach cramps or nausea.

The CDC report did not state how many of the illnesses were linked to people who ate at Schnucks salad bars but said a majority of those in initial interviews were linked to nine locations for “grocery store Chain A.” Schnucks confirmed it was that chain. The CDC believes the contaminated lettuce was eaten between Oct. 5 and Oct. 24.

The CDC said public health investigators used DNA “fingerprints” taken from stool samples to identify cases linked to this outbreak.

Victims ranged in age from 1 to 94, and 63 percent were female.

The CDC said romaine lettuce served at the salad bars all came from “a single lettuce processing facility via a single distributor. This indicates that contamination of romaine lettuce likely occurred before the product reached grocery store Chain A locations.”

To help avoid E. coli, health officials encourage people to wash hands thoroughly, especially after going to the bathroom; wash produce and cooking equipment; and cook all meats to at least 167 degrees, the level at which germs are killed.

Health officials estimate there are 70,000 E. coli infections each year in the U.S., though many infected people don’t seek medical care and are not tested for E. coli.