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Introducing our dirtiest public objects

New testing on gas pumps and mailboxes, among other things in six major U.S. cities, will make you want to wash your hands before checking your e-mail.

Poor mail carriers. Not only do they have to put up with threatening dogs and foul weather, but they spend their days touching what may be one of our dirtiest everyday objects: mailbox handles.

The only worse offender? Gas pump handles.

Experts say regular hand-washing goes a long way. SCA Svenska Cellulosa Aktiebolaget/Flickr

So says a new study by researchers at hygiene solutions firm Kimberly-Clark Professional, who took more than 350 swabs from a variety of everyday objects in Atlanta, Chicago, Dallas, Los Angeles, Miami, and Philadelphia to measure ATP (Adenosine Triphosphate) levels commonly used to detect contamination.

While they did not distinguish between contamination types (i.e. molds versus bacteria), they did measure contamination levels, marking those with ATP levels above 300 as the dirtiest.

Also high on the list: escalator rails, ATM buttons, parking meters/kiosks, and vending-machine buttons. This introduces a whole new way of looking at too much driving and vending-machine food being bad for our health.

In the past, many studies have focused on in-home and in-office surfaces, such as keyboards (some of the dirtiest items) and toilet handles (some of the cleanest, possibly due to being more frequently cleaned). Public surfaces, on the other hand, have yet to be studied as extensively.

"There's an awful lot in the literature about the home environment and places where contamination can occur, and there's a real push to use home hygiene to prevent the spread of illness, but people often don't bring into that public places where you can encounter that contamination, and then bring it into your home," says Dr. Kelly Arehart, a program leader for the company's Healthy Workplace Project.

So if contaminants are so abundant on everyday objects, why care? We're clearly able to live with them.

"My first reaction [to that argument] is that there are times and ages when you might not be as concerned about your health, but as a carrier, you can affect those you come into contact with," said Jim Mann, executive director and chief science officer of the Handwashing for Life Institute. "Those in the healthier age bracket have strong immune systems, so it hasn't been a problem for them. But when you consider the amount of damage to people who are sick and dying, it becomes more important."

Dr. Arehart goes so far as to call diligent hand-washing a "civic duty," and her Healthy Workplace Project colleague Brad Reynolds lays out the following common scenario: "We ran some pilots last year from November 1 through April 30. We took 40,000 ATP swabs, and we found that, far and away, the dirtiest things in the office, without exception, were the computer keyboards. They are dirtier than the mouse, phone, and desk, and they are certainly dirtier than toilet seats in all office buildings we looked at. First thing people do in the morning is check e-mail. First thing after getting back from a meeting is check e-mail. Then they eat lunch at their desk."

If those people pumped gas, checked their mail, or used an ATM on the way to work, they are bringing the outside world directly to their desks and colleagues. The biggest takeaway, the researchers suggest, is to perform diligent hand-washing, if only as a common courtesy to one's co-workers.