Whether you’re slicing them up for a salad or topping a burger — tomatoes are a summer staple. But, the popular fruit is now at the center of a huge 30-state salmonella outbreak.

According to the Centers for Disease Control and Prevention, more than 20 people have been hospitalized and at least one person has died since mid-April.

And while federal health officials still don’t know the exact source – they have narrowed the outbreak down to three types of raw tomatoes: red plum, red Roma or round red tomatoes.

The problem is — there is no way for consumers to detect salmonella (you can't smell, taste or see it).

But, fortunately there are some things you can do reduce the risk:

CHECK YOUR TOMATOES

The Food and Drug Administration is advising people to eat only tomatoes not associated with the outbreak: cherry tomatoes, grape tomatoes, tomatoes sold with the vine still attached and tomatoes grown at home.

For other tomatoes, wash thoroughly and cut away the part that is attached to the plant and the button on the other side, said Julie Miller Jones, a professor of nutrition and food science at The College of St. Catherine in St. Paul, Minn. That part can carry a foodborne illness because it's a hard area and organisms can attach themselves to it, she added.

Also, cooking tomatoes at 145 degrees will kill salmonella.

INQUIRE AT RESTAURANTS

Ketchup and cooked sauces are not affected by the outbreak. And several restaurants are not serving tomatoes — on Monday, McDonald's said it had stopped serving sliced tomatoes in its U.S. restaurants. Burger King, Outback Steakhouse and Taco Bell have also voluntarily pulled tomatoes from their menus.

If you are really concerned, tell the restaurant to leave the tomatoes off the sandwiches and salads, said Jones. Even if you remove them once your order comes, the food could still be contaminated, she said.

REPORT THE ILLNESS

Many people misdiagnose salmonella poisoning as the flu, said Jones. Salmonella poisoning generally occurs hours after ingestion, she said, and involves symptoms such as abdominal cramps, headache, fever, diarrhea, nausea and vomiting.

The CDC said symptoms generally appear 12 to 72 hours after infection. People should report a suspected foodborne illness to the local health department.

WASH PRODUCE

Wash all produce, whether organic or not, with cold running water, said Jones. Scrub them gently with your hands or with a vegetable brush. Remove outer layers of cabbage and lettuce.

Fruits should be washed, regardless of whether you are eating the peel, said Al Baroudi, president of Food Safety Institute (FSI) International. He said even if someone is peeling an orange, that person is touching part of the orange he is going to eat. (Bananas are an exception.)

Don't bother with a special vegetable wash, said Jones. She said studies show that it's not much better than water.

WASH HANDS, SURFACES

Wash your hands with soap and water thoroughly before handling food, said Blakeslee. Wash your hands if you come in contact with pet feces, use the bathroom or change a baby's diaper.

Also wash cutting boards, counters and utensils to avoid cross-contamination. Avoid any kind of contact with raw meat when preparing fresh vegetables. Refrigerate sliced up fruits and vegetables.

For more information:

U.S. Food and Drug Administration (FDA)

Centers for Disease Control and Prevention (CDC)

The Associated Press contributed to this report.