Washington, May 3 (Reuters): Worried about colds, flu and other germs? Go ahead and touch those doorknobs and elevator buttons, but watch out for the telephone, fresh laundry and sinks, a top expert advises.

And while you should always wash your hands before making a meal, many people do not realise that they should do so afterwards also, says Charles Gerba, a microbiologist and clean water expert at the University of Arizona. “Most of the common infections ? colds, flu, diarrhea ? you get environmentally transmitted either in the air or on surfaces you touch. I think people under-rate surfaces.”

And when they are cautious, they are usually cautious about the wrong things. Germs do not stick where people believe they will.

“Doorknobs are usually on the low side,” said Gerba.

A recent informal survey of a Reuters office helped him illustrate how microbes take advantage of misconceptions to propagate themselves.

Two computer keyboards, for example, carried far more bacteria than an elevator button, the handles and button on the communal microwave oven or the office water fountain, Gerba’s lab found.

Keyboards and telephones ? especially when they are shared ? are among the most germ-laden places in a home or office, Gerba said. “Keyboards are a lunch counter for germs.... We turn them over in a lot of studies and we are amazed at what comes out of a keyboard.”

In fact, the average desk harbours 400 times more bacteria than the average toilet seat, says Gerba, whose latest survey focuses on the germiest professions. “Nobody cleans the desktop, usually, until they stick to it,” he says.

Perhaps not surprisingly, teachers have the highest exposure to bacteria and viruses, Gerba has found. Accountants, bankers and doctors also tend to have microbe-laden offices, while lawyers came out surprisingly clean in the germ-count stakes.

Gerba’s lab does a simple overall bacteria count for its most general surveys. The person swabs each surface and sends it to Gerba’s lab, which then cultures the bacteria in a lab dish.

The growth of whatever bacteria are present can be used to estimate an overall load of germs, including harmless E. coli bacteria ? which are found in the gut and are an indicator of what scientists delicately call “fecal contamination”.