So how many people have human papillomavirus in their mouths?
Quite a few, say researchers who got more than 5,000 volunteers across the country to spit into a cup and answer detailed questions about their sex lives.
The bottom line: 6.9 percent of people in the U.S. (ages 14 to 69) have oral infections with HPV. Some types of HPV are linked to cancer and genital warts.
About 3.7 percent of people have "high-risk" oral infections from types of HPV that are most likely to lead to cancer. About 3.1 percent have "low-risk" infections.
A dramatic increase in cancers of the head and neck has been linked, in part, to HPV, which is also a cause of many cervical cancers. Now we have some real numbers about the extent of infection in the U.S. to go on.
For instance, a virus type dubbed HPV-16 was found to affect about 1 percent of people. That's the one that's been detected in about 85 percent of oral cancers.
There were some other noteworthy findings. Men are much more likely to have an oral HPV infection than women (10.1 percent vs. 3.6 percent). And people who have had more sex partners and more frequent sex are more likely to be positive for HPV.
Merck and GlaxoSmithKline make vaccines against HPV. The vaccine is recommended for girls and, recently, boys to guard against cancers of the cervix and anus, as well genital warts.
But the vaccines aren't approved to prevent oral cancers. And the researchers note that the vaccines' effectiveness against oral HPV infections is "unknown, and therefore vaccination cannot currently be recommended" to prevent oral cancers.
Ohio State's Dr. Maura Gillison, lead author of the paper, has served as a consultant to both Merck and Glaxo. Merck was one of the funders the study.