Every day, parents blithely drop their toddlers into the baskets of shopping carts, never giving a moment’s thought to who might have had their hands on the handle last. Preliminary results from a new study show that may be a mistake.

Researchers from the University of Arizona swabbed shopping cart handles in four states looking for bacterial contamination. Of the 85 carts examined, 72 percent turned out to have a marker for fecal bacteria.

The researchers took a closer look at the samples from 36 carts and discovered Escherichia coli, more commonly known as E. coli, on 50 percent of them — along with a host of other types of bacteria.

“That’s more than you find in a supermarket’s restroom,” said Charles Gerba, the lead researcher on the study and a professor of microbiology at the University of Arizona. “That’s because they use disinfecting cleaners in the restrooms. Nobody routinely cleans and disinfects shopping carts.”

The study’s results may explain earlier research that found that kids who rode in shopping carts were more likely than others to develop infections caused by bacteria such as salmonella and campylobacter, Gerba said.

Shopping cart handles aren’t the only thing you need to worry about when you go to the local supermarket, Gerba added. In other research, he’s found that reusable shopping bags that aren’t regularly washed turn into bacterial swamps. “It’s like wearing the same underwear every day,” Gerba said.

The best way to keep kids safe, Gerba said, is to swipe the shopping cart handle with a disinfecting wipe before you pop your kid into the basket.

That's exactly the option some supermarkets were offering even before the study was done.

"We saw that this was something our customers were concerned about," said Libba Letton, a spokesperson for Whole Foods Market stores. "So we make disposable wipes available for customers coming into the store with shopping carts."

Letton said the company doesn't routinely wash down carts themselves unless something has been obviously spilled on them.

Risk to kids?

One thing Gerba couldn’t say was how likely it was that a child would get sick from touching — or even sucking on — a contaminated handle.

As far as Dr. Neil Fishman is concerned, that risk isn’t very big. “I’d be worried if there was any evidence of any disease outbreaks related to shopping cart use,” said Fishman, an infectious disease expert and director of health care epidemiology and infection prevention at the University of Pennsylvania Health System. “There isn’t — and we’ve been using them for a long time.”

While there may, indeed, be bacteria on shopping cart handles, they can also be found on doorknobs, countertops and a host of other items we touch every day, Fishman said. “My guess is that there are more bacteria on a car seat than on a shopping cart,” he added.

Ultimately, your only defense against germs is to keep your hands — and your kids’ hands — squeaky clean, Fishman said.

“While you can’t sterilize your environment, you can limit exposure by practicing good hand hygiene,” he added. “For most cases, alcohol hand rubs are the best for every day use.”