ATLANTA -- It's the beginning of the summer, and it's tough to find fresh salsa for our chips and tomatoes for our burgers.

And a federal government that's been sluggish in the past is being more responsive, consumer advocates said. It hasn't been pretty, however. It's been a little like trying to cut a tomato with a dull knife.

On Tuesday, federal authorities cleared fresh tomatoes being harvested in Florida and all those grown in California -- the nation's top two tomato-producing states -- of responsibility in the national food poisoning scare, which has sickened 167 people since April.

It's an expensive proposition to toss seemingly edible food, experts said. But McDonald's and others had good reason to pull the tomatoes, said Bill Marler, a Seattle attorney who for 15 years has specialized in food-contamination cases.

"The dilemma is if they don't recall the tomatoes and someone gets sick, then they're going to really look foolish," he said.

The government was still trying to pinpoint the source of the dangerous bacteria Tuesday.

"It's narrowing down rapidly. We hope that in the next few days we'll be in a position to identify the exact source," U.S. Food and Drug Administration Commissioner Andrew von Eschenbach said while speaking at the Commonwealth Club in San Francisco.

Asked if the contaminated tomatoes could have come from overseas, he said: "That's one of the possibilities. That's certainly one of the things we're looking at."

The FDA was posting on its Web site states and countries that had safe tomatoes.

U.S. health officials said there were no confirmed salmonella deaths linked to the outbreak, which was reported in at least 17 states. Fewer than 200 people turned up sick.

But some contrasted this produce scare to earlier ones that produced more tepid reactions. In 2006, the last prominent outbreak of salmonella associated with tomatoes, at least 183 illnesses occurred in 21 states. That outbreak was blamed on tomatoes eaten in restaurants. But restaurants didn't stop serving tomatoes back then.

Experts cited a range of possible explanations for the difference, including the FDA's quick and specific action.

"This outbreak, the FDA is clearly making an effort to do better to inform consumers," said Sarah Klein, attorney in the food-safety program for the Center for Science in the Public Interest, a consumer advocacy group. "They have been fairly slow in the past.

But experts acknowledged the current situation is complicated, with companies making announcements at a time some might consider either too late or too early: Too late, in that the outbreak appears to be winding down, with no new illnesses occurring in two weeks. And too early, in that health investigators have not yet pinned down a particular food outlet, distributor or grower as a source of the contaminated tomatoes.

For their part, restaurant chains said they were simply being cautious.

"This action is being taken as a precautionary measure to ensure the safety of our guests," said Burger King Corp. spokeswoman Denise Wilson.

McDonald's spokesman Bill Whitman said the restaurant chain made the decision to recall tomatoes with "an abundance of caution." He noted that McDonald's also wasn't implicated in any way in the recall or asked to stop selling tomatoes.

Asked if McDonald's has lowered the bar for when it yanks foods or ingredients, Whitman said: "We're always trying to improve on our own standards."

Meat has been a sensitive topic for restaurant chains after a 1993 outbreak in which four children died and hundreds of people became ill after eating undercooked hamburgers from Jack in the Box restaurants.

But some believe food sellers have become increasingly sensitive to the issue of contaminated produce since 2006, when spinach contaminated with E. coli bacteria killed three people and shook consumer confidence in green leafy vegetables.

"The spinach outbreak was very influential," said Dr. Patricia Griffin, who oversees foodborne illness investigations at the Centers for Disease Control and Prevention.

The FDA has been communicating with food industry groups about the outbreak. But no one within the agency consulted specifically with McDonald's before the company made its decision to pull tomatoes, FDA spokeswoman Kimberly Rawlings said.

Federal investigators know that certain types of tomatoes are safe -- such as cherry and grape -- and certain locales are safe because harvest times and distribution patterns don't match the salmonella outbreak, said Dr. David Acheson, the FDA's assistant commissioner for food protection.

Salmonella is a bacterial infection that lives in the intestinal tracts of humans and other animals. The bacteria are usually spread by eating foods contaminated with animal feces.

Most infected people suffer fever, diarrhea and abdominal cramps starting 12 to 72 hours after infection. The illness tends to last four to seven days.

Many people recover without treatment. However, severe infection and even death is possible. Infants, the elderly and people with weakened immune systems are at greatest risk for severe infections.

Health officials say they are aware of 13 tomato-associated outbreaks since 1990. The largest was in 2004, when more than 500 cases occurred in at least five states, linked to a convenience store chain.

• AP writers Matthew Perrone in Washington, Dave Carpenter in Chicago and Laura Wides-Munoz in Miami contributed to this report.

On the Net: www.fda.gov/oc/opacom/hottopics/tomatoes.html