(Nov. 13) The latest incident of foodborne illness came and went before the public realized it had happened, and although federal investigators are blaming restaurant tomatoes as the cause of a salmonella outbreak, they’re not sure which restaurants are the source.

The outbreak occurred from Sept. 14 to Oct. 1, with one case reported Oct. 14. More than 180 people in 21 states, and two people in Canada, became sick.

“There is no risk to the public as far as this risk is concerned,” said Christopher Braden, chief of outbreak response and surveillance at the Centers for Disease Control and Prevention’s Foodborne Branch, during an early November news conference.

Because the outbreak has only been linked to restaurants so far, it appears the tomatoes are somehow different than those found in retail stores, Braden said. He said that if the outbreak had involved all tomatoes it would be even more difficult to trace where the contamination came from.

“Even though we know the outbreak was caused by the consumption of tomatoes, we believe that any tomatoes that could have been implicated in the outbreak have been destroyed, thrown out or eaten,” said David Acheson, chief medical officer for the Food and Drug Administration. “Based on that, we don’t believe there is a need to issue a specific warning to consumers.”

In past outbreaks, Acheson said the FDA was able to trace back to particular states and, on occasion, to a series of farms, but he wasn’t aware of having narrowed the search down to a specific farm, as was the case during the E. coli outbreak involving spinach.