South Plainfield, N.J. ? Taco Bell ordered scallions removed from its 5,800 U.S. restaurants Wednesday after tests suggested they may be responsible for the E. coli outbreak that has sickened at least three dozen people in three states.

The fast-food chain said preliminary testing by an independent lab found that three samples of green onions appeared to have a dangerous strain of the bacterium.

“In an abundance of caution, we’ve decided to pull all green onions from our restaurants until we know conclusively whether they are the cause of the E. coli outbreak,” said Greg Creed, president of Irvine, Calif.-based Taco Bell.

The company would not immediately identify the supplier of the scallions, so it was unclear whether contaminated green onions reached other restaurants or supermarkets.

Tainted green onions from Mexico were blamed for a 2003 outbreak of hepatitis A in western Pennsylvania that was traced to a Mexican restaurant. Four people died and more than 600 people were sickened after eating the green onions at a Chi-Chi’s.

California is the nation’s largest supplier of green onions. But by December, with winter setting in, the vegetable is often imported from Mexico.

At least 46 confirmed cases of E. coli sickness linked to Taco Bell have been reported in New Jersey, New York and Pennsylvania.

All 15 Taco Bell restaurants in Philadelphia voluntarily closed Wednesday following a recommendation by the city’s Department of Public Health.

Two restaurants on New York’s Long Island were also closed Wednesday for cleaning. The chain, a subsidiary of Yum Brands Inc., had reopened other restaurants there linked to the outbreak. A Taco Bell in New Jersey remained closed for cleanup. Two other Taco Bells in New Jersey that were implicated never closed.

In Trenton, Nidhi Trikha stopped by an unaffected Taco Bell for a quick lunch Wednesday that included a chicken quesadilla and a bean chalupa – but no green onions.

After hearing about the outbreak, she said she was sorry she ate.

“I know fast food is always unhealthy, but it’s quick and cheap,” she said. “God, I hope I’m OK.”