Given how often they're on the floor, occasionally inside a public restroom, it should come as no surprise that a third of women's purses crawl with E. coli.

And given how many grubby hands and baby bottoms touch grocery store shopping carts, we shouldn't flinch at the fact that, on average, they carry 115 times more bacteria than a toilet seat.

It's a dirty world we're living in, and often our germiest encounters are not where we expect them. Not all germs are harmful, and healthy bodies can resist many illnesses. But the more people are exposed, the greater their chance of becoming infected with or transmitting a dangerous bug, from respiratory viruses to a host of foodborne bacteria. The Centers for Disease Control and Prevention estimates that each year 48 million Americans, or 1 in 6 people, get sick, 128,000 are hospitalized, and 3,000 die of foodborne diseases.

"You're always gambling with germs," said Dr. Charles Gerba, professor in the department of soil, water and environmental science at the University of Arizona. "The thing is to make the odds in your favor."

That means reducing exposure to germs, a feat best accomplished with regular hand-washing, using hand sanitizer and keeping your paws off your face, Gerba said.

It also means cleaning those grimy items you rarely think to clean, like remote controls and cellphones.

How often to scrub down depends on several factors. If you have kids or pets, if you are immunocompromised or someone in your household is sick, you may need to clean more thoroughly and frequently, said Donna Duberg, assistant professor of clinical lab science at Saint Louis University in St. Louis.

Need motivation? Here are average total bacteria counts, per square inch, for a dozen common germ-infested items we encounter in our daily lives, according to Gerba, who has tested hundreds of surfaces.

775,460,560

Dish sponge

The dirt: Easily the grossest cesspool in your household, the sponge is often a culprit in spreading germs around when you use a dirty one to "clean" other surfaces. It takes about a week for the germ count to get sky high.

To clean: Some people suggest running sponges through the dishwasher, but Duberg cautions that can contaminate your dishwasher and your dishes. Better to throw them away and buy a new pack at the dollar store, she said. You could also put it in the microwave for 30 seconds to kill germs, Gerba said. Do this weekly or after each time you wipe down surfaces that had raw meats or vegetables on them.

228,854

Kitchen faucet handle

The dirt: There's more fecal bacteria in the kitchen sink than in the toilet after we flush it, Gerba said, thanks to all the meat and produce remnants that collect there.

To clean: Clean off visible soil first, then wipe with sanitizing wipes. The surface must stay wet for 30 seconds to kill 99.9 percent of germs, Duberg said.

138,000

Shopping cart

The dirt: Exposed to food and infants, as well as birds in the parking lot, shopping carts are dirtier than many other public surfaces. Coliform bacteria were detected in 72 percent of 85 shopping carts sampled in a study. Children have been found to be at higher risk of salmonella infection when riding in a cart, Gerba said.

To clean: Carry sanitizing wipes with you and wipe down the handle and the basket where kids tend to sit. Avoid rubbing your face, and wash your hands afterward.

79,000

Keyboard/mouse

The dirt: Janitors rarely touch your personal space, so if you don't clean it, no one will.

To clean: Use sanitizing wipes to wipe every surface of the keyboard (use cotton swabs to get between the keys) and mouse and all around your workstation. Do it at least weekly, or more if you are sick or other people use the computer.

61,597

Cutting board

The dirt: Raw meat and chicken can make cutting boards a dangerous source of cross-contamination if they're not cleaned properly.

To clean: For wooden boards, scrub with hot soapy water to remove soil, then do it again to kill bacteria, Duberg suggests. Plastic boards can go in the dishwasher or be soaked in a 10 percent bleach (which must then be rinsed off with soapy water) or 10 percent vinegar solution.

50,068

Bathroom faucet handle

The dirt: Bathrooms overall had less bacteria than kitchens, where constant contact with food adds to cross-contamination, according to one of Gerba's studies.

To clean: Wipe with sanitizing wipes at least weekly or as needed.

17,000

Remote control

The dirt: Given that they pass between many hands, are used while snacking and rarely get cleaned, remote controls are often germ baths.

To clean: Wipe with sanitizing wipes a couple of times per week.

11,020

Cellphone

The dirt: Pressed against your face and mouth all day, cellphones can give germs easy access to enter your body. It's particularly hairy if you share your phone.

To clean: Wipe with a sanitizing wipe daily.

8,643

Doorknob

The dirt: Though they get a bad rap, things like doorknobs and light switches usually aren't so dirty, because people aren't touching them very often.

To clean: Wipe with a sanitizing wipe at least weekly, more often if you are ill.

4,500

Self-checkout touch screen

The dirt: Touched by thousands of strangers and rarely cleaned.

To clean: Rub your hands with hand sanitizer after using, allowing them to stay wet for 30 seconds to kill bacteria.

1,736

Kitchen countertop

The dirt: When you bring foods and meats into your kitchen from the grocery store, open and clean them in an area away from where you prepare food, and put them into clean containers before storing them.

To clean: Create your own cleaning solution consisting of 10 percent white distilled vinegar and 90 percent water and put it in a spray bottle. Spray the counter to saturate completely, let it sit for 30 seconds to kill the germs, then wipe off. Unlike bleach solutions which only keep for 24 hours before losing effectiveness, vinegar solutions keep indefinitely and needn't be washed off, Duberg said.

1,201

Toilet seat

The dirt: Because people are careful to disinfect the toilet seat regularly, it tends to be among the cleanest surfaces in the house.

To clean: Wipe with sanitizing wipes as needed, letting it stay wet for at least 30 seconds. One gross thing to keep in mind is that flushing the toilet releases bacteria-laden aerosols that settle on bathroom surfaces. So consider keeping your toothbrush in a drawer.

• Read more articles by ALEXIA ELEJALDE-RUIZ

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