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Kim Painter, Special for USA TODAY

A nice firm handshake has long been a mark of good manners and elevated social skills.

It is also a very germy way to greet your fellow humans, much worse than a couple of more casual alternatives, a new study shows.

'A short, sweet fist bump will transmit the least bacteria,' and even a high-five is better than a traditional shake, says David Whitworth, a senior lecturer in biochemistry at Aberystwyth University-Ceredigion in the United Kingdom.

Whitworth and a colleague systematically tested the three greetings for a study published Monday in the American Journal of Infection Control.

For the experiment, one of them repeatedly dipped a gloved hand into a container loaded with a not-too-dangerous strain of E. coli bacteria. The dirty-gloved scientist let the film dry, then shook, fist-bumped or high-fived the other person's clean, gloved hand. Finally, the receiving gloves were tested for bacteria.

Result: The shakes transmitted about 10 times more bacteria than the fist bumps and about two times more than the high fives. The longest, firmest shakes transmitted the most.

In a separate round in which the gloves were dipped in paint rather than bacteria, the researchers found one rather obvious explanation: Bigger areas of the hands touched during the shakes. Handshakes also tended to last longer, but the researchers found more clinging germs even when they compared shakes to fist bumps and high-fives of the same duration.

Since we don't go around dipping our hands in vats of bacteria, the experiment does not perfectly mimic real life in which different areas of the hand carry different amounts of bacteria, for one thing. It does provide some new ammunition for those who would like to ban handshaking in hospitals and other places where germs are a particular concern.

Whitworth says it also provides an especially good alternative, the fist bump. 'You can't really imagine a world where people don't greet each other physically,' he says. 'It seems to be a basic human need.'

Whitworth's findings 'are not surprising,' says Mary Lou Manning, an associate professor in the school of nursing at Thomas Jefferson University in Philadelphia and president-elect of the Association for Professionals in Infection Control and Epidemiology.

She is not enthusiastic about replacing handshakes with fist bumps in hospitals. The better, more hygienic idea, she says, is to promote rigorous hand-washing and ban hand-to-hand greetings altogether. 'That's already starting to happen' in a lot of places, she says.

She says she 'can't even imagine' health workers and patients greeting one another with a casual fist bump. A nod or slight bow might be nicer, she says.

Whitworth concedes that the perceived informality of fist bumps and high fives might be a problem. Figures as august as President Obama and the Dalai Lama have used them, he notes 'but I couldn't imagine the British prime minister doing that.'

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