The next time a man hands you a hot dog after making a run to the restroom and the concession stand at an Atlanta Braves baseball game, be careful: there is a good chance he did not wash his hands, according to a report released Monday by a group that sends spies into public restrooms in the name of science.

Only about two-thirds of the men observed washed their hands after using the restroom at Turner Field — the lowest rate for any of the locations cited in the observational study and survey on the hand-washing habits of Americans. The study, conducted every few years, was released by the American Society for Microbiology and the American Cleaning Institute at a microbiology conference in Boston.

Some subjects were asked about their washing habits in telephone interviews; others were watched by undercover observers in public restrooms. Some of what the sink spectators witnessed was, well, filthy. Consider: 20 percent of people using the restrooms at Pennsylvania Station and Grand Central Terminal in New York did not wash their hands.