WASHINGTON (Reuters) - Tomatoes eaten in restaurants were probably the source of an outbreak of Salmonella food poisoning that sickened 183 people in 21 states and Canada, federal health officials said on Friday.

The outbreak is over and is no longer a threat, the U.S. Centers for Disease Control and Prevention said. But 22 people were sick enough to be admitted to hospitals, the CDC's Dr. Christopher Braden, Chief of Outbreak Response and Surveillance, told reporters.

"We identified tomatoes eaten in restaurants as the cause of this outbreak," Braden told a telephone briefing.

Braden said there was no evidence pointing to any single restaurant or type of restaurant.

"From what we can see, it's across the board," he said.

Salmonella can cause serious and sometimes fatal infections in young children, frail or elderly people, and others with weakened immune systems. It can cause fever, bloody diarrhea, nausea, vomiting, and abdominal pain.

"Now that we have a specific food commodity, FDA has initiated a trace-back," Dr. David Acheson of the U.S. Food and Drug Administration told the briefing. He said the FDA would try to find where the restaurants had purchased their tomatoes.

"In particular, FDA is working closely with the states of Minnesota, Massachusetts, and Connecticut, since groups of illnesses were specifically reported in these states," the agency said in a statement.

Outbreaks of foodborne illness have made headlines in the United States. In August and September an outbreak of E. coli bacteria in baby spinach sickened 300 people and killed three.

Reuters