If you want to lower your odds of getting the flu — which has sickened more than 20 million U.S. residents since last October, according to estimates from the Centers for Disease Control and Prevention — work on improving your hand-washing technique. Scrub your hands for at least 20 seconds, using soap and clean water, either warm or cold. No watch or tech-device timer handy? Just hum the song “Happy Birthday to You” twice, from start to finish. Be sure to wash your fingertips, between your fingers and under your nails — not just the palm and back of your hands. Then rinse and dry. Sounds simple, but 2013 research from the Journal of Environmental Health notes that only 5 percent of people wash their hands the right way — and for long enough — to kill the germs and bacteria that reside on hands. (That data came from researchers who watched more than 3,700 people at the sinks in public restrooms.) Over the years, various studies have found that, at any given moment, hundreds (if not thousands) of germs populate people’s hands. including E. coli. People touch something that has germs on it — a doorknob or a handrail, for instance — and then touch their eyes, nose or mouth before washing their hands. Shaking hands or hugging can help the germs spread from person to person. Preparing food or drinks with unwashed hands can do the same. Besides the flu virus, these germs can lead to colds, lung infections, diarrhea, hepatitis, meningitis and more. But only 20 seconds of good hand washing — done frequently, especially during cold and flu season — can help stem the spread. If water isn’t available, an alcohol-based hand sanitizer will work.