The FDA initially issued a warning June 3 about tomatoes in New Mexico and Texas. Saturday, officials expanded the warning nationwide.
There were 25 hospitalizations but no deaths. The cause is a rare strain of salmonella called Salmonella Saintpaul.
"We're trying to get an answer as quickly as possible as to where these tomatoes came from," says David Acheson, director of the FDA's Food Safety and Security Staff.
The FDA hasn't been able to track the source of the contaminated tomatoes to a single grower or packer or even a specific geographic area. It is working with the Centers for Disease Control and Prevention, state health departments and the food industry to track the cause of the outbreak.
States reporting illnesses linked to the outbreak include Arizona, California, Colorado, Connecticut, Idaho, Illinois, Indiana, Kansas, New Mexico, Oklahoma, Oregon, Texas, Utah, Virginia, Washington and Wisconsin.
Cherry tomatoes, grape tomatoes, tomatoes sold with the vine still attached and home-grown tomatoes are not associated with the outbreak, Acheson says.
FDA officials are still determining the type of tomatoes involved in the outbreak, but the agency's preliminary investigation suggests that raw red plum, red Roma or round red tomatoes are the culprit.
Salmonellosis in healthy people can cause fever, diarrhea (which can be bloody), nausea, vomiting and stomach pain.
"It's not something that you'd want," Acheson says. "It's going to land you with two or three days of a lot of discomfort."
In most healthy adults, the illness will "run its course at home. They're not going to require antibiotics," he says.
Salmonellosis can be dangerous to young children, the elderly or people with weakened immune systems. For young children especially, dehydration is an issue. The FDA recommends that if people in these groups get the illness, a health care professional should be contacted immediately.
Cooking tomatoes at 145 degrees for at least 15 seconds will probably kill the bacteria.
Simply washing tomatoes can help, but it won't necessarily remove the salmonella bacteria, because when tomatoes are picked on very hot days and put into cold water to chill, salmonella on their surface can be drawn up into the fruit.
That doesn't mean the public should stop washing produce, Acheson says. "If there is surface contamination, washing is going to help remove it."