As the number of people sickened by a salmonella outbreak continues to rise, federal officials say they are no longer certain that tomatoes are the cause of the illness.

Almost three months after the outbreak began on April 10, officials with the U.S. Food and Drug Administration and Centers for Disease Control and Prevention are no closer to tracing the source of the problem, which has now sickened 810 people.

''Whatever this produce item is that is causing the illness, it is still out there getting people sick,'' Dr. Patricia Griffin, chief of the CDC's Enteric Diseases Epidemiology Branch, told reporters Friday on a conference call. "We have no evidence that the outbreak is over."

The latest victim got sick on June 15 — well after the FDA warning prompted grocers and restaurateurs to pull three of the most popular types of tomatoes off their shelves and menus.

While Griffin says there remains a ''strong association'' between tomatoes and salmonella, the CDC has an "open mind about other possibilities and looking into other ingredients.''

She wouldn't comment on what those potential items might be but said that a number of patients reported eating fresh salsa and guacamole before becoming sick.

"Produce investigations are very difficult because most of the time vegetables are all eaten together," Griffin said.

The possibility that tomatoes might have been wrongly targeted as the cause of the salmonella outbreak raised the ire of Florida's tomato growers. They've watched their business drop by as much as 50 percent in the last month. The longer it takes to find the source of the outbreak, the worse things are expected to get.

''This is absolutely nuts,'' said Tony DiMare of DiMare Farms, whose family is one of the biggest tomato growers and packers in Florida and the country. ``Our industry has been tainted, and we have been devastated financially. They don't even know what they're looking for. It's a witch hunt.''

Even as the search broadens, warnings about what consumers should eat haven't changed, said Dr. David Acheson, Food and Drug Administration food safety chief.

Grape tomatoes, cherry tomatoes and tomatoes on the vine have never been associated with the outbreak. Raw red round, Roma and plum tomatoes should be consumed only if they come from areas deemed safe by the FDA. The 19 counties in Florida that were producing tomatoes during June have been ruled safe.

Acheson also warned that the FDA may never be able to figure out the source of this outbreak because of the way tomatoes are packed and repacked. It's not uncommon for tomatoes from multiple farms to be placed in the same box and sent to a retailer or restaurant.

In the past week, the FDA has sent investigators to farms and packing houses in Florida and Mexico, searching for the cause of the salmonella. This search has included areas in Central and South Florida, although Acheson wouldn't reveal locations or the places visited.

An initial 1,700 samples have all come back negative, with no traces of the strain of Salmonella Saintpaul, Acheson said. Hundreds of additional samples are still being tested.

''It's possible this investigation will not ultimately provide a smoking gun that allows us to pinpoint the source of the contamination,'' Acheson said.

At this point there may be multiple sources — somewhere between the farm and the table — causing the outbreak. The FDA is investigating the possibility that contamination could be happening during the packing or distribution process.

Hampering the investigation is the fact that Florida farms under investigation stopped growing tomatoes months ago and many of the fields are already plowed under. In those cases the FDA is looking for evidence in the water supply and environmental contamination.

"The colder the trail gets, the less likely you are going to be to find the problem," Acheson said. "But that's not a reason not to try."

Florida's tomato growers are tired of the waiting, which is costing them millions of dollars in lost revenues. And they've already started demanding that this case result in dramatic changes at the FDA.

"What Hurricane Katrina was to FEMA this salmonella outbreak is going to be to the FDA," said Bob Spencer of West Coast Tomato in Palmetto. "There's got to be more prudence in ringing the alarm bell. They've got to know what they're talking about before they go to the public and identify the cause of an outbreak."

Florida tomato growers already have the support from members of Florida's congressional delegation, who have been calling for the FDA to find the salmonella source and do a better job of informing the public of what's safe.

"Their handling of this has really been completely unsatisfactory," said U.S. Rep. Debbie Wasserman Schultz, a Democrat who represents a district north of Miami. "They seem like they have a lackadaisical attitude about what this is doing to the tomato industry.''

She and North Florida Democratic Rep. Allen Boyd, who are on the powerful House appropriations committee, hope next month to offer an amendment to an agricultural spending bill that would prod the FDA to study the traceback program they use in cases like the latest outbreak.

Acheson already agrees that there is a need for change. "We've got to improve the process because the one that we're operating under right now is clearly not getting us answers fast enough," he said. "If we're going to do the best job of protecting public health, we have to identify the source as quickly as possible so we can put a stop to the problem at the root cause."