"I'd go back to the bottle of water," Gerba said.
These innocuous-looking offenders are difficult to avoid, which is part of the reason why push buttons can be crawling with germs.
Further, ubiquitous buttons, found on ATMs, elevators, telephones and drink machines, among other things, are located in areas that are not often cleaned and disinfected to kill bacteria and viruses.
Gerba noted that the first-floor buttons in elevators were the dirtiest.
"Everyone needs to go to the first floor," he said.
Worse, these germs get transferred to the body part that comes in contact with faces the most -- fingers and hands.
While avoiding these types of buttons can be almost impossible, Gerba does have a few recommendations.
"Knuckle it or wait for someone else to push it for you."
Sweating it out with a yoga session can be a great way to cleanse the mind and body, but forget to cleanse your mat, especially a communal one, and all that work may have been for nothing.
Sweat and microbes can cover an exercise mat during a workout. This may not be a problem if the mat was cleaned and disinfected before and after each use and laundered sporadically. But if the mats are not cleaned, germs can linger for days.
According to a 2006 article in The New York Times, gyms and yoga studios vary in terms of how often and how well they clean their mats. Some put the onus on patrons by providing disinfecting wipes.
And while thin booties and gloves are sometimes marketed as no-slip yoga accessories, they serve well to protect feet and hands from germ-ridden mats.
For any gym activity, Gerba recommends wiping equipment and hands frequently with gel sanitizers containing alcohol or other disinfecting agent.
"These are probably the worst," Gerba said. "They are the germiest restrooms you'll run across."
But bathrooms in general are not as germ-ridden as other areas -- a kitchen sink or laundry machine, for example. Compared to several items on this list, toilets are a beacon of cleanliness because they are cleaned and disinfected on a regular basis, even public toilets.
Airplane bathrooms get cleaned, but the high volume of people they must cater to in a short amount of time leaves them very dirty very quickly.
Gerba said a normal aircraft has one bathroom per 50 people. Discount airlines have one bathroom per 75 people.
"There is a thin layer of E. coli over the sink," and other surfaces, Gerba said, adding that many people, especially men, will not wash their hands effectively because the sink is small, and dirty hands transfer germs to the face easily.
Interestingly, the cleanest toilets are probably those in public areas of a hospital, Gerba said.
"In a city, I'd pull into the emergency room."
An individual probably has a fairly short interaction with the shopping cart at the local grocery store. Unfortunately, that interaction covers all the danger zones for contamination: hands, faces and food.
In one study done by his group, Gerba said he found E. coli on almost half the shopping carts the group tested. These are the microbes and pathogens that are transferred from the cart to your hands, to the food you select and then to the face if the hands touch it.
In addition, children often sit in the seat provided in larger shopping carts, adding to the germ load on the cart.
"That's putting a kid's butt where you put your broccoli," Gerba said.