Produce other than tomatoes is being examined by U.S. officials stymied in their efforts to find the source of a salmonella outbreak that has sickened 869 Americans.

Tomatoes suspected to have caused the outbreak may have been contaminated by contact with other produce, officials of the Food and Drug Administration and Centers for Disease Control and Prevention said Tuesday on a conference call with reporters.

The number of people who have become ill since the outbreak began in April is a record for salmonella cases associated with produce, according to the CDC, and is more than four times the 205 cases reported after packaged fresh spinach was tainted by E. coli in 2006. The tally of illnesses grew by 59 since June 27, and 107 of the cases led to hospitalization. Officials, saying they are frustrated, widened their focus.

"There is clearly a need to think beyond tomatoes," said David Acheson, the FDA's associate commissioner for foods who has led the investigation. "The tomato trail is still hot. It's a question of whether other items are getting hotter."

One possibility is that tomatoes were cross-contaminated by other produce from the same or adjoining farms or shared water sources, he said. Common packing, distribution or shipping facilities might also spread the contamination among different produce generally served with tomatoes, he said.

It would be "irresponsible" to identify what other kinds of produce may be implicated until more testing is done, Acheson said. The expansion will increase the laboratory workload, so FDA activated its "food emergency response network" of 100 labs run by federal and state governments, said Acheson. The network was used during the spinach crisis.

Acheson said he was frustrated by the pace of the investigation, a sentiment shared by U.S. Health and Human Services Secretary Mike Leavitt at a media briefing Tuesday.

"Nothing happens fast enough when you have a problem like this," Leavitt said. "This is a problem of enormous complexity. We will find what the source of it is, and we will learn from this."

Investigators have identified "clusters" of illnesses from certain regions and are trying to use those cases to trace the cause, according to the FDA.

The agency is at fault for failing to develop a reliable "traceability system" to uncover sources of contamination, said Rep. Rosa DeLauro, D-Conn., in a statement Tuesday.

"Nearly three months into this investigation, new cases of salmonella continue to be diagnosed — some of whom fell ill less than two weeks ago — consumer confidence further erodes, and the food industry faces estimated costs of at least $100 million," DeLauro said.

Federal health officials began warning consumers on June 3 to avoid raw red plum, red Roma and red round tomatoes, as well as products containing them, until the outbreak is contained. Consumers were advised Tuesday that cherry and grape tomatoes and those sold with the vine attached weren't likely to be tainted with salmonella.

Of the total reported thus far, 179 people first became ill after June 1, said Robert Tauxe, deputy director of CDC's foodborne disease division, in the conference call. More than 80 percent of them consumed fresh tomatoes, making that vegetable the prime suspect, he said.

FDA officials have said they believe the outbreak involves tomatoes grown in Mexico or Florida, and investigators are checking points along the distribution chain from those locations. Samples of tomatoes taken during the investigation have tested negative.

Tomatoes have been shipped from Mexico to Florida, combined with Florida tomatoes, and packaged together, complicating the FDA's investigation, Acheson said. In other cases, tomatoes were shipped from Florida to Mexico for packaging, and then shipped back to the U.S.

If the tomatoes are from locations listed as cleared on the FDA's Web site, the products are safe to eat. If they aren't on the list or vendors don't know where they're from, the tomatoes shouldn't be consumed, the FDA says.

Most people infected with salmonella have diarrhea, fever and cramping for four to seven days and recover without treatment. The people most susceptible to hospitalization or death are infants, the elderly and people with impaired immune systems.