Los Angeles ? An E. coli outbreak linked to Taco Bell restaurants left the fast-food chain with a major damage-control challenge Thursday: How can it reassure customers its food is safe even as the suspected cause of the outbreak remained unconfirmed?

The outbreak has left more than four dozen people sick in at least three states. Taco Bell ordered the removal of green onions from its 5,800 restaurants nationwide Wednesday after testing by an independent lab suggested the bacteria may have come from scallions.

Analysts said the Mexican-style restaurant chain is likely to see sales decline in the short term.

“You’ve got a crisis of confidence right now,” said Michael Sitrick, a crisis-management expert. “What they need to do to bring people back in the stores is to assure them that what happened in the past cannot happen in the future.”

Taco Bell, an Irvine, Calif., unit of Yum Brands Inc., told customers that in addition to getting rid of all its green onions, it sanitized the affected restaurants and set up a toll-free number for people to call with concerns.

Paul Argenti, a business professor at Dartmouth College in Hanover, N.H., said Taco Bell appeared to be doing a good job handling the problem.

“When you’re in the middle of it, give people any information that you know, as much as possible,” he said. “Try to be honest and open and transparent.”

Argenti said he believes a television ad campaign to reassure customers is not necessary. Taco Bell has a loyal customer base that “will be looking for a reason to go back,” he said. “Within six months, everything rights itself.”

Taco Bell spokesman Rob Poetsch said the chain is preoccupied with the investigation. He would not say if it plans a major publicity effort. The restaurant is working as closely as possible with authorities “to find the root cause of this,” he said.

Also Thursday, federal health officials were monitoring two more suspected cases of E. coli in Utah and South Carolina. Officials said the South Carolina man may have fallen ill after eating at a Taco Bell in Pennsylvania. And in Delaware, all 14 Taco Bell restaurants closed for cleaning after a 15-year-old girl who ate at a Taco Bell in New Jersey was hospitalized.

The company suggests that customers who are worried about the outbreak call its hot line, (800) TACO-BELL.

Barry Sawyer, an operator who answered the phone at the Miami-based call center, said he has handled 25 calls since Wednesday. Most callers were not ill; they just wanted to understand the situation.