Published: Jul 19, 2010 11:52 PM EDT
Updated: Jul 19, 2010 7:39 PM EDT

FORT MYERS, Fla--It's the first thing you order when you go to a restaurant, but the last thing you think would give you food poisoning. We're talking about: your soft drink.

The results of our CALL FOR ACTION investigation uncovers some disturbing news about fountain drinks...that may have you asking your favorite restaurant some tough questions about what's in your cup!

To see how it could happen, CALL FOR ACTION went undercover through drive thrus and into convenience stores. We bought 15 different common soft drinks. Then we bottled them up and sent them to EMSL lab in Orlando to have them tested.

"We found that 25 percent of them had bacteria," said Dr. Blanca Cortez who tested our samples.

Three of our 15 samples had high levels of yeast and mold.

"If you have someone who is quite sensitive to it, you are going to have either diarrhea. If you're allergic: a mild case of food poisoning," said Cortez.

That's not all we found.

One sample had staph. In another one, scientists detected fecal material.

"Food poisoning can occur when you have staphylococcus areas and certainly some bad case of diarrhea with the fecal chloroform. Just in general: it's poor hygiene," said Cortez.

Cortez says soda is naturally acidic, which means it is really hard for bacteria to grow because the acid kills it. But if it is dirty enough to get started, soda contains so much sugar the mold and yeast has enough food to grow.

"How does it get to a soda place?," said Cortez, "My feeling is it's handling. People touch the nozzles. They're not careful and they're cross contaminating."

The good news: most of the samples we collected came back completely clean. That shows it's certainly not impossible to keep bacteria out of your soda.

One of the restaurants that passed our test was the Hardee's on Palm Beach Boulevard. We asked owner Mike Justice how he does it.

"It's very simple," said Justice, "Every night, the nozzles are all taken off. They're washed. They're dried. Dispensers are wiped down weekly. We take the beverage bar apart. Wash sanitize everything in it. It's very simple simple maintenance. Just hot water is all you need to do to keep 'em clean."

So what can you do you do to protect your family? Both Cortez and Justice say it's simple common sense.

"You have to be able to trust the place where you buy your soft drink," said Justice, "If the machine doesn't look clean, it's probably not. It's very simple."

Both Cortez and Justice says look around the restaurants you visit and ask yourself: "Is it clean?" If you can see the soda fountains, are they dry? Sitting water provides a great environment for bacteria to grow.