About 7 percent of adults and teens in the United States are orally infected with the human papillomavirus, or HPV, a new study says. This represents about 14.9 million people.
More men are affected than women: About 10 percent of men ages 14 to 69 have an oral HPV infection, compared with 3.6 percent of women, the study showed.
Oral HPV infections cause some oropharyngeal cancers, or cancers of the tongue, the tonsils or back of the mouth. People who are infected with the strain HPV 16 are 14 times more likely to develop these cancers compared with those not infected with the virus.
The new findings were "reassuring," according to study researcher Dr. Maura Gillison, chair of cancer research at The Ohio State University , because they show that while oral infection with the virus is common, cancer cases as a result of these infections are rare. In other words, most infected people don't get cancer. The American Cancer Society estimates there will be about 40,000 new cases of cancer of the oral cavity and pharynx in 2012.
The findings also show oral HPV infections are, for the most part, sexually transmitted. People who reported engaging in oral sex were twice as likely to have an oral HPV infection as those who did not engage in oral sex. People who had had sex of any kind, including vaginal sex or oral sex, were eight times more likely to have an oral HPV infection than those who had not had sex. Among those who'd had 20 or more sexual partners, one in five had an oral HPV infection.
"Taken together, these data indicate that transmission by casual, nonsexual contact is likely to be unusual," the researchers wrote in their study.
However, there are clues HPV may also spread by kissing. Oral HPV infections were more common among sexually experienced people who had not engaged in oral sex than among sexually inexperienced individuals, a finding that is "consistent with transmission by other sexually associated contact (eg, deep kissing)," the researchers wrote in their study.
"This study of oral HPV infection is the critical first step toward developing potential oropharyngeal cancer prevention strategies," Gillison said. "This is clearly important, because HPV-positive oropharyngeal cancer is poised to overtake cervical cancer as the leading type of HPV-caused cancers in the U.S."
More studies are needed to know whether the HPV vaccine effectively prevents oral HPV infections, the researchers said. Currently, the vaccine is recommended to prevent cervical cancer, anal cancer and genital warts.
How common is oral HPV?
Between 1998 and 2004, incidence of new cases of oropharyngeal cancer in the United States more than tripled (from 0.8 cancers per 100,000 people to 2.6 cancers per 100,000 people).
Despite the rise, little was known about the prevalence of oral HPV infection, and the characteristics of those who have it.
In the new study, Gillison and colleagues analyzed data from more than 5,500 men and women in the United States. Participants answered questions about their sexual behavior and substance use. They were also asked to gargle mouthwash for 30 seconds, and cells that were exfoliated into the rinse were analyzed for evidence of HPV infection.
The researchers found HPV in the cells of 6.9 percent of the participants, and HPV 16 in 1 percent.
The infection was most common among those ages 60 to 64 years, (at 11.4 percent), and those ages 30 to 34 (at 7.3 percent).
Physicians should encourage their patients who engage in oral sex to use barrier protection, Dr. Hans P. Schlecht, of the Drexel University College of Medicine, Philadelphia, wrote in an editorial accompanying the study.
Smokers and alcohol users also had a high prevalence of HPV. About 20 percent of those who said they smoke 20 or more cigarettes per day had oral HPV infection.
It's not clear why oral HPV infection was more common among men than women. It could be that HPV is more likely to be transmitted through oral sex on women versus men, the researchers said. Differences in hormone levels between the sexes could also affect the duration of an infection.
Smoking may suppress the immune system, leading to longer infections with the virus, the researchers said.
The researchers noted their findings are based on study participant's reports of their sexual behavior and smoking, which may not be completely accurate.
Researchers need to follow people over time to better understand the effects of age, gender, sexual behavior and smoking on the incidence and duration of oral HPV infections, the researchers said.
The study will be presented this week at the Multidisciplinary Head and Neck Cancer Symposium in Phoenix. The study and editorial are published online on Jan. 26 in the Journal of the American Medical Association.
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