BY SHARI ROAN
LOS ANGELES TIMES/MCT
A new study showing an estimated 7 percent of American teens and adults carry the human papillomavirus in their mouths may help health experts finally understand why rates of mouth and throat cancer have been climbing for nearly 25 years.
The evidence makes it clear that oral sex practices play a key role in transmission.
The new data, published online last week by the Journal of the American Medical Association, is the first to assess the prevalence of oral HPV infection in the U.S. population.
Traced to oral sex
The findings indicate that the virus is not likely to spread through kissing or casual contact and that most cases of oral HPV can be traced to oral sex, which many Americans mistakenly view as a safe practice.
“There is a strong association for sexual behavior, and that has important implications for public health officials who teach sexual education,” said Dr. Maura L. Gillison of the Ohio State University Comprehensive Cancer Center, who led the study and presented the findings on Jan. 26 at a meeting of head and neck cancer researchers and doctors in Phoenix.
Though herpes, HIV and other diseases can be transmitted via oral sex, the practice is often considered a safer alternative to sexual intercourse.
A survey released last year by the U.S. Centers for Disease Control and Prevention found that about 90 percent of adults have had oral sex, along with 27 percent of 15-year-old boys and 23 percent of 15-year-old girls.
“I donâ€™t think people think of oral sex in the same way they do with traditional intercourse,” said Fred Wyand, director of the HPV Resource Center at the American Social Health Association in Research Triangle Park, N.C.
“Sometimes younger people engage in oral sex so they donâ€™t have to worry about pregnancy. They may not even make the link between oral sex and STDs.”
Suspicion among researchers that the behavior could cause oral cancers by transmitting HPV to the mouth has been mounting over the last decade.
Initial studies found that patients with oral cancer were far more likely than healthy controls to have engaged in oral sex. And a 2007 study in the New England Journal of Medicine found that the more oral sex partners a person has had, the greater their risk of developing throat cancer.
Most oral HPV infections are harmless, and oral cancers are still relatively uncommon. But given the new information, doctors should encourage their patients to use protection during oral sex, Dr. Hans Schlecht, assistant professor of medicine at Drexel University College of Medicine in Philadelphia, wrote in an editorial accompanying the study.
“Itâ€™s something people are not comfortable talking about, but it is protective,” he said in an interview.
“If you are going to be intimate with someone, there are some adult conversations you need to have.”
HPV is best known as the cause of cervical cancer, which kills 4,220 women in the U.S. each year, according to the National Cancer Institute. The virus can also cause vulvar, anal, penile and various head and neck cancers.
A study published in October in the Journal of Clinical Oncology traced more than 70 percent of new cases of oral cancers to HPV infection, putting it ahead of tobacco use as the leading cause of such cancers.
If present trends continue, HPV will cause more cases of oral cancers than cervical cancer by 2020, according to the October study.
HPV infection is common â€“ an estimated 80 percent of Americans have contracted the virus, Gillison said. It usually produces no symptoms and is typically cleared from the body through natural processes.
But persistent infections can cause cancer. Vaccines are now available for children and young adults to prevent cervical and anal cancers caused by the most troublesome HPV strains.
To get a handle on HPVâ€™s role in oral cancers, Gillison and her colleagues analyzed data from 5,579 people ages 14 to 69 who participated in the National Health and Nutrition Examination Survey in 2009 and 2010.
The NHANES survey includes a detailed questionnaire and a physical examination, including the first large-scale use of a 30-second oral rinse from which researchers were able to extract cells to test for HPV infection.
The test, which can detect the virus in the mouth as accurately as in the cervix, was 10 years in the making.
Gillisonâ€™s team found that the overall prevalence of oral HPV was 6.9 percent â€“ far less than the rate of genital HPV infection in reproductive-age women, which can be as high as 42 percent among women in their 20s.
The infection rate varied substantially among different groups. For instance, 10.1 percent of men in the study had oral HPV, compared with 3.6 percent of women. The reason for the difference is unknown but it could have to do with oral sex practices, Gillison said.
Among people who had more than 20 sexual partners, the prevalence of oral HPV was 20 percent. But the researchers found it in less than 1 percent of people who said they were virgins and in less than 4 percent of people who said they had never performed oral sex.
Researchers also noted age differences; those in the early 60s had the highest prevalence at 11.4 percent. That is in marked contrast to cervical HPV infection, which is most common among women in their early 20s.
Itâ€™s unclear why the prevalence of oral HPV peaks much later in life, Gillison said. One possibility is that the immune system weakens with age, making people more vulnerable to latent infections. Another theory is that study participants in their 60s grew up during an era of sexual permissiveness that preceded public-health messages about safe sex.
“People who came of age during the sexual revolution may have had more sexual partners than other age groups, such as groups that came of age during the HIV epidemic,” Gillison said.
More to consider
In the meantime, the new data should give parents more to think about as they consider whether to vaccinate their children – especially their sons, Gillison said.
HPV vaccination is recommended for females ages 9 to 26 and males ages 9 to 21.
“Some parents may have felt that the risk of HPV infection wasnâ€™t relevant to them,” she said. “But this study shows 1 in 10 boys has an infection that can lead to a cancer.”