LOS ANGELES (Reuters) - The source of the Salmonella that has sickened hundreds of people through tainted tomatoes may be in Mexico and South and Central Florida, U.S. investigators said on Friday.

A pile of tomatoes are seen on display at a wholesale produce market in Washington, June 12, 2008. REUTERS/Jim Young

Health officials said all indications pointed to a single geographic region as the source of the outbreak, which has sickened 228 people in 23 states.

David Acheson, associate commissioner for foods at the U.S. Food and Drug Administration (FDA) said on a conference call that nine people who became ill with Salmonella had eaten at two different outlets of the same restaurant chain. He declined to name the chain or the location of the restaurants. “That represents a small cluster within this outbreak,” he said.

The outbreak has been disastrous for the U.S. tomato industry, which produced $1.28 billion of the fruit last year.

The FDA has linked the outbreak to raw round, plum and Roma tomatoes, and has issued a list of states and countries whose tomatoes are not associated with the outbreak.

California, Georgia, New York, Canada, Guatemala and the Dominican Republic are among tomato producers on the safe list. The FDA also has cleared counties in North Florida, whose tomatoes were not widely available at the time of the outbreak.

The FDA said investigators were focusing on South and Central Florida and Mexico because they were the biggest producers at the time.

The Mexican government says its tomatoes are being unjustly targeted and notes that the uncommon Salmonella Saintpaul bacteria identified in the outbreak has never been found in Mexico.

The agriculture ministry said in a statement on Friday it would send a delegation to the United States next week to press officials there to declare Mexican tomatoes as safe to eat.

“The borders have not been closed to Mexican tomato imports but the alert put out by the U.S. government had provoked a decline in consumption,” the ministry said.

Some shipments from Mexico have been stopped at the border by worried importers, raising concern among some analysts that Mexico could be hit by a glut of rejected produce.

The Florida Tomato Committee said on Thursday the state’s industry remained committed to production of a safe product. It said Florida was the first state in the country to adopt a comprehensive food safety program with mandatory government inspection and audit of its tomatoes.

FOOD-BORNE ILLNESS

Salmonella bacteria are frequently the culprit for food-borne illnesses. Symptoms of infection include fever, diarrhea, nausea, vomiting and abdominal pain and generally appear within 12 to 72 hours of eating tainted food.

Infants, the elderly and those with weakened immune systems are more likely than others to develop severe illness.

Salmonella infections commonly result from eating food that has been contaminated by animal feces, but it is also caused by human feces.

The U.S. Centers for Disease Control and Prevention said there have been at least 13 multi-state Salmonella outbreaks linked to different types of tomatoes since 1990.

The FDA is under increasing pressure from consumer groups and Congress to do more to protect the U.S. food supply. Responsibility for protecting food is split among the FDA, the U.S. Department of Agriculture, the Centers for Disease Control and Prevention, and state regulators.

Food safety officials have said that outbreaks of food-borne illnesses are rare.

One of the worst outbreaks in the United States in recent times was caused by tainted spinach in 2006. That E. coli outbreak killed three people and sickened more than 200.