Bad enough when the recent salmonella outbreak was blamed on tomatoes, but now federal authorities are worried about all the ingredients in fresh salsa and pico de gallo. So what's a scared chip-dipper to do? And how worried should anybody be?

Here's what we know:

Q: What is salmonella and why should I care?

A: Salmonella is the name of a family of bacteria that lives in the digestive tracts of many kinds of animals. More than 2,000 varieties have been identified in humans. Some make people sicker than others, but the basic symptoms are the same: diarrhea, fever, and abdominal cramps 12 to 72 hours after infection. The illness usually lasts four to seven days.

Q: How do people get infected?

A: As Dr. Douglas Powell, scientific director of the International Food Safety Network, puts it: "Follow the poop." The only way to catch salmonella is to eat foods that have been in contact with excretion from an infected animal. Many illnesses come from insufficiently cooked meat or eggs. Vegetables can't be infected but can be tainted from sources that include droppings from a passing bird or lizard onto a growing plant, tainted water used to irrigate a field or to wash picked crops, or food handlers who didn't wash their hands after touching something that contained the bacteria.

Q: When did this outbreak start?

A: The first reports started showing up in April. Investigators identified the infection as a previously rare strain of the bug. By comparison, only six infections with saintpaul salmonella were identified during April through June of 2007.

Q: I thought authorities had blamed tainted tomatoes for this outbreak. What happened?

A: Federal health authorities had issued a "mission accomplished" in early June when they put out the warning about tomatoes but had to back down when reports of new infections continued to come in.

Q: Why has it been so hard to figure out the source of the infection?

A: Can you remember exactly what you had for lunch last Wednesday? How about dinner? How about the next day? Multiply that by more than a thousand cases scattered through 41 states, the District of Columbia and Canada. An infection can take as many as three days to produce symptoms. Getting medical attention, plus the series of tests needed to identify the particular strain of infection, can take another couple of weeks. By that time, investigators must depend on the memories of ill patients and have little chance of finding actual samples of tainted food.

Q: Who is at greatest risk of getting a severe salmonella infection?

A: Otherwise healthy adults almost always recover completely without treatment after a few unpleasant days. But the very young, the elderly, and those with other health problems can get sick and even die.

Q: How can I kill salmonella at home?

A: A quick dip of fresh foods into a weak solution of bleach — one tablespoon per gallon — will do the trick. Rinse the bleach off in running water. Cooking any food to 165 degrees will kill the bugs — but only if you are sure the entire pot gets that hot. A brisk rinse in running water won't kill bacteria but can wash most of them off the food, some experts say.

Q: If cooking works, why doesn't the "heat" in hot peppers kill salmonella?

A: The culinary burn is caused by capsasin, a natural chemical that experts say does not affect salmonella in the relatively small concentrations found in most foods.

Q: I've heard that cilantro kills bacteria. Why would authorities be worried about tainted cilantro?

A: One study showed that cilantro might kill some germs. "Maybe that works in the test tube," said Dr. Michael Doyle, director of the Center for Food Safety at the University of Georgia. "But in the real world, cilantro has been shown to be a carrier of salmonella."