LOS ANGELES — An estimated 7 percent of American teens and adults carry the human papilloma virus in their mouths, an infection that puts them at heightened risk of developing cancer of the mouth and throat, researchers said Thursday.

Their study, the first to assess the prevalence of oral HPV infection in the U.S. population, may help health experts understand why rates of oropharyngeal cancer — a type of head and neck cancer — have skyrocketed in recent years, increasing 225 percent between 1988 and 2004.