OLYMPIA, Wash. -- Health officials have linked nine cases of E. coli infection in Western Washington to contaminated lettuce.

Three people in Thurston County and six people in Pierce County were infected. Some of those infected were hospitalized, the state Health Department said. A 10th case may be linked, but was not tested.

VIDEO: Tainted Romaine Lettuce Linked To E. coli Cases

Health officers said three teenagers were served tainted romaine lettuce at Capital High School in Olympia.

The Thurston County Health Department said a student at Thurgood Marshall Middle School also became sick.

State health officials said the six Pierce County victims ate the tainted lettuce at a college and at a restaurant.

"This is a product that will be at a restaurant, a cafeteria or a food vendor. This is not a product that would be coming from a grocery store," said Dr. Marcia Goldoft, Acting Epidemiologist of the Washington Department of Health.

Goldoft said all the victims became sick last month and that there have been no new cases in two weeks.

"We have no evidence this is an ongoing outbreak," she said.

The Food and Drug Administration is working to trace the source of the disease, health officials said.

In 1993, three children died and hundreds of people were sickened by E. coli in the Pacific Northwest. The source of the contamination was traced to contaminated beef at Jack-in-the-Box restaurants.