In a telephone survey, 91% of adults claimed to always or usually wash their hands after using a public restroom. But only 83 percent of the adults observed (90% of women and 75% of men) actually did wash their hands.

The survey was released Wednesday by the American Society for Microbiology and the Soap and Detergent Association, a trade group, in honor of Clean Hands Week.

The US Centers for Disease Control and Prevention maintains that hand washing is the single most important thing you can do to prevent colds, flu and foodborne illness. Others agreed.

Single Most Important Health Practice

"Eighty percent of all infections are transmitted by direct and indirect contact," said Dr. Philip Tierno, director of clinical microbiology and immunology at New York University Medical Center in New York City and author of five books, including The Secret Life of Germs and Protect Yourself Against Bioterrorism.

"If this is the profound statement that we have to work with, then it stands to reason the single most important thing anybody can do for themselves to protect health and safeguard themselves against unnecessary infection is washing your hands," he continued.

But not just any hand washing: Tierno recommends washing for 40 seconds or longer -- enough to sing "Happy Birthday" twice. The CDC, on the other hand, will accept a 20-second wash.

The studies released Wednesday looked at hand washing without a time limit. One was an observational study to assess what people are really doing, and the other was a telephone survey of more than 1,000 adults designed to find out what Americans said they were doing.

For the first study, more than 6,300 individuals were observed as they washed or didn't wash their hands in restrooms at different public attractions in four major cities: Atlanta's Turner Field, Chicago's Museum of Science and Industry and Shedd Aquarium, New York City's Grand Central Station and Penn Station, and San Francisco's Ferry Terminal Farmer's Market.

Gender Gap

Overall, 83 percent of adults (90 percent of women and 75 percent of men) observed did wash their hands. In the telephone survey, however, 91 percent of adults claimed to always or usually wash their hands after using a public restroom.

The worst hand hygiene habits were found at Turner Field, where 26 percent of sports fans did not wash their hands (84 percent of women did wash their hands vs. just 37 percent of men). Presumably, the majority of stadium goers are men.

San Francisco's Ferry Terminal Farmers Market scored the best, with 88 percent of men and women washing their hands.

New York's Penn Station had the greatest gender gap, with 92 percent of women washing up, compared with only 64 percent of men.

At Shedd Aquarium in Chicago, 89 percent of adults (85 percent of males and 93 percent of females) washed their hands, while at Chicago's science museum 87 percent (81 percent of males and 93 percent of females) washed their hands.

In the public restrooms at New York City's Grand Central Station, 79 percent of all adults (67 percent of men and 89 percent of women) washed their hands.

Perception-Reality Gap

On the phone, the picture appeared brighter, with 83 percent saying they washed their hands after using the bathroom at home, 77 percent before handling or eating food, and 73 percent when changing a diaper.

On the other hand, only 42 percent said they washed after petting a dog or cat, 21 percent after touching money and a mere 32 percent after coughing or sneezing.

And the perception-reality gap was more pronounced among men, 88 percent of whom said they washed their hands after using a public restroom when only 75 percent were actually seen doing it. Ninety-four percent of women said they washed their hands while 90 percent were actually caught in the act.

The proportion of people seen washing their hands rose slightly in this survey, up from 78 percent in 2003. This was apparently due to an increase among females (83 percent to 90 percent) vs. males (74 to 75 percent).

The picture is also brighter than that found in 2003 in US airports. There, more than one in five travelers neglected to use the sink, and protect themselves and others against infectious germs.

More information: Find more about washing your hands at the American Society for Microbiology.