This next story may not be the best dinner table conversation but it will give you pause the next time you put your paws on the salt and pepper shaker or crack open a menu. As elisabeth leamy found... See More
This next story may not be the best dinner table conversation but it will give you pause the next time you put your paws on the salt and pepper shaker or crack open a menu. As elisabeth leamy found out going undercover when it comes to eating out have some purel on standby. Reporter: We wanted to get the dirt on dining out. While you're feasting, where are the germs festering? We tested ten surfaces at ten restaurants in three states to find out. What is this tiny little thing? A hidden camera that looks like a button. Just pop it right into this purse, and no one will ever suspect! Does bacteria congregate on the condiments? Check out that goo. Reporter: Or pull up a chair and join you at the table? I don't know when they last wiped this. Visible grunge on here. Reporter: Is that salmonella perched on the edge of your glass, or is she in the bathroom with her friends? Reporter: Look at that. This is sticky to the touch! Lab testing by dr. Philip tierno and his team at the nyu microbiology department revealed visible goop didn't always translate into bad bugs, but some spotless surfaces harbored major microbes. So it's fair to say that the danger is real? No one is saying you should live in a bubble, but you should be aware of how we spread germs and where germs lodge. Reporter: We quizzed people on the street and found they have no clue. What do you think is the germiest thing in a restaurant? That would be the garbage. Reporter: You're probably right. So what's the real dish? Here's our restaurant confidential countdown. Number 10, the salad bar tongs just weren't that bad -- maybe because americans don't eat enough salad. In ninth place, ketchup bottles weren't harboring anything too awful. I'm somewhere between the ketchup and the bathroom doorknob. I'm going to go with the -- well, we call it taps, but faucets. Reporter: Believe it or not, bathroom knobs and faucets ranked just eighth and seventh in our countdown. The faucets, the door handles were some of our least germy items. We think we know why. Because they get cleaned. Really? That's surprising to hear! Reporter: Then there's number six. Glass rims. Our tests detected multiple bacterias including one linked with tuberculosis. Worse yet, we caught waiters on tape gripping our glasses right at the top where we drink, which gives those pathogens a direct route into our bodies. We know that the number one cause of death in the world is germs. Reporter: That may sound dramatic to you, but not to heidi bulk. It felt like something was inside me tearing me to shreds. Reporter: The college athlete got so sick and so weak, that an ambulance raced to get her to the hospital. Heidi couldn't eat for 10 days and lost 15 pounds. The diagnosis? A severe salmonella infection after eating her only meal of the day at a restaurant. This was hands down the sickest I've ever been. I was at that level of sick where you start getting really concerned about how much long you have to endure this or if you're going to get to endure it. Reporter: Back to our countdown. Number five, as the numbers go down, those nasty germs go up. Now, restaurant tables. What you are saying is we may be bringing the germs in with us? It's both. It's the waiters, it's the restaurant, it's the person who is frequenting the restaurant. A potty problem at the point. Reporter: Like the parents who thought it was okay to change their baby's diaper at the table or toilet train their toddler right in the restaurant. But wait, there's more! Number four, salt and pepper shakers. Fully half of those were contaminated because they're used so often but rarely cleaned. To be even more disgustingly specific, one of the most frequent contaminants was fecal matter. Ugh. That's terrifying to know. Reporter:50 percent of lemon wedges were tainted with human waste too, but we ranked them number three because of this. The lemon is already in my glass. So if there's bacteria on it, there's nothing I can do. So how does that unmentionable stuff get on lemons in the first place? We caught restaurant workers grabbing lemons with their bare hands reaching in again and again without gloves or tongs. The root of the problem is bad hand washing. So I came here to the university of maryland's food safety laboratory to prove a point. I'm going to put e. Coli bacteria all over my own hands. And then wash for just seven seconds with no soap because studies show that's exactly what most americans do. And finally, I rub my hands on this petri dish. Next I repeat the entire process with the e. Coli, only this time I use soap and lather for the entire 20 seconds that experts recommend. And just wait till you see the difference in what grows! Time now for number two on our countdown. I'd say this because everyone looks at that. I think the menu. Reporter: Ding! High-five. Yep, you may get more than you ordered off of the menu. We found the bacteria that caes staph infections on one and the germs that cause strep throat on another. So how do you protect yourself? We're back at the lab and I have something to show you. When I washed my hands for just seven second, look at this moonscape of filth that was still left on my hands. But when I washed thoroughly for 20 seconds, check it out, clean petri dish, clean hands! And that's a relief as we reveal the number one source of germs at the restaurants we tested. Something not one person guessed. Would you like to have a seat? Yes, I would! Reporter: Ah. I just noticed something. When you touched that seat, if you were at a restaurant, did you ever think that it would be covered in germs? No. Reporter: Yes! 70 percent of the seats we tested had bad bacteria on them. 17 different kinds! Including strains of the deadliest of all, e. Coli. Why? Because all customers sit on them, and most restaurants don't think to sanitize them. Not very appetizing, is it? Not at all. Reporter: Bon appetit. It's gross! Reporter: So what can you do? It's simple. The next time you go to a restaurant and take a seat, order your food, then go wash your hands, before you eat.
This transcript has been automatically generated and may not be 100% accurate.