THURSDAY, June 19 (HealthDay News) -- The number of people known to have fallen ill after eating salmonella-tainted tomatoes has now jumped to 383 in 30 states plus the District of Columbia, U.S. health officials announced Wednesday afternoon.

"The marked increase is not due to new infections but mainly because some states improved surveillance in response to this outbreak and laboratory identification of many other previously submitted strains has now been completed," said Casey Barton Behravesh, an epidemiologist with the U.S. Centers for Disease Control and Prevention, during a teleconference. "We now have reports of at least 48 persons being hospitalized due to this illness."

The ages of the patients range from under 1 to 88 years old, and 47 percent of them are female. The most recent onset of illness was June 5; the outbreak was first discovered in April.

"We are continuing to receive reports of ill people," said Dr. Robert Tauxe, deputy director of the CDC's division of foodborne, bacterial and mycotic diseases. "We do not think the outbreak is over."

Tauxe also could not say if the outbreak had peaked yet, given that some states are still catching up on necessary laboratory work. "I would say that the majority of new cases had onset around three to four weeks ago, but some new cases onset in the last two to three weeks that might suggest that there are still some cases continuing to occur," he said. "It's too early to call the peak, and we certainly cannot say that it's over."

On Thursday, health officials again repeated that the outbreak may not be over.

"We are still characterizing this outbreak as ongoing. There may be other cases out there," Ian Williams, chief of the CDC's OutbreakNet Team, told reporters at an afternoon teleconference. "It's evolving. We're watching the numbers come in on a daily basis, and we expect to see the numbers increase," he said.

There was, however, no added victim count on Thursday afternoon.

And officials have still not zeroed in on the exact source of the contamination, although on Thursday, Dr. David Acheson, associate commissioner for food protection at the U.S. Food and Drug Administration, appeared to rule out any connection to Mexico.

"FDA has no information that the outbreak strain has been linked to tomatoes from Mexico. Nor does FDA know of any cases of salmonella linked to the outbreak in Mexico," Acheson said.

Health officials last week had said that the bulk of the tomatoes available at the start of the outbreak in April had come from Mexico and parts of Florida.

On Wednesday, Acheson seemed less certain than he has in the past that the exact source would ever be identified. "I have to acknowledge that we may not ultimately know the farm where these came from," he said. "But we're continuing to go flat-out, assuming we are going to get to that point."

A cluster of nine cases still holds promise for helping to break the deadlock. But a second patient has retracted the original information he or she gave the FDA on where contaminated tomatoes were eaten, basically rendering that particular "trace-back" effort worthless, officials acknowledged.

Acheson would not confirm that this cluster of nine cases was the same as a cluster being investigated in Chicago that originated at two Adobo Grill restaurants.

Meanwhile, restaurants and supermarkets across the country are starting to sell and serve tomatoes again. The Chicago Sun-Times reported that McDonald's restaurants are bringing back some tomatoes, as is Wendy's and Burger King. Yum Brands, which owns Taco Bell, KFC and Pizza Hut, is also bringing back tomatoes from "safe" areas, the newspaper said.

"I can't speak to why one chain is going back and one isn't," Acheson said. "From a food-safety perspective, I'd like retailers to put tomatoes on the menu but make sure they come from a safe place. They do need to know their suppliers."

Acheson also said that the FDA has asked for authority to take action to prevent future outbreaks. "We have put the word out that we need authority to require preventative control," he said. "Exactly what that would look like would depend exactly on what the legislation looked like. But at a high level, we feel we need preventative control for high-risk foods, and tomatoes and other types of fresh produce would be part of that."

Currently, the U.S. agriculture industry relies on a set of voluntary "good practices" to ensure food safety.

"We have asked for authorities, and we don't yet have them. What we're looking for here is mandatory. There would be no voluntary about it," Acheson said.

In other developments, the Seattle Post-Intelligencer reported on its Web site Wednesday that more than 8,000 people may have actually been sickened in this salmonella outbreak. The explanation: "Based on earlier extensive studies and extrapolations, the CDC has estimated that for every one case of salmonellosis reported, there are 38 additional cases that are not reported," according to the newspaper site.

Williams appeared to confirm the theory Thursday.

"For every case we see, there are 30 cases we don't see," Williams said. "There are probably thousands of cases."

Salmonella is a bacteria that can cause bloody diarrhea in humans. Some 40,000 cases of salmonellosis are reported in the United States each year, although the CDC estimates that because milder cases are not diagnosed or reported, the actual number of infections may be 30 or more times greater. Approximately 600 people die each year after being infected.

More information

Visit the U.S. Centers for Disease Control and Prevention for more on the salmonella outbreak.