A new study suggested that an estimated 7% of American teens and adults carry the human papillomavirus in their mouths. This may help health experts finally understand why rates of mouth and throat cancer have been climbing for nearly 25 years. The evidence additionally makes it clear that oral sex practices play a key role in transmission.
This was reported online Thursday by the Journal of the American Medical Assn. and is the first to assess the prevalence of oral HPV infection in the U.S. population. 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.
“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 Thursday at a meeting of head and neck cancer researchers and doctors in Phoenix.
Experts say that although 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% of adults have had oral sex, along with 27% of 15-year-old boys and 23% of 15-year-old girls.
“I don'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 Assn. in Research Triangle Park, N.C. “Sometimes younger people engage in oral sex so they don't have to worry about pregnancy. They may not even make the link between oral sex and STDs.”
However the link between oral cancers and transmission of 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.
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% of new cases of oral cancers to HPV infection, putting it ahead of tobacco use as the leading cause of such cancers.
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. “It'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 infection is common — an estimated 80% 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.
For this new study 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 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.
Gillison's team found that the overall prevalence of oral HPV was 6.9% — far less than the rate of genital HPV infection in reproductive-age women, which can be as high as 42% among women in their 20s. The infection rate varied substantially among different groups. For instance, 10.1% of men in the study had oral HPV, compared with 3.6% 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%. But the researchers found it in fewer than 1% of people who said they were virgins and in fewer than 4% of people who said they had never performed oral sex.
Researchers also noted age differences: Those in their early 60s had the highest prevalence at 11.4%. That's in marked contrast to cervical HPV infection, which is most common among women in their early 20s. The reason is unclear. 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.
The study also linked heavy smoking to oral infection. It's possible that smoking weakens the body's immune response, making it easier for an infection to persist.
Dr. Peter Leone, medical director of the North Carolina HIV/STD Prevention and Control Branch, said these data point to shifts in patterns of sexual practices in the U.S. “With the era of HIV, we've seen a movement of heterosexuals engaging in more oral sex with the idea that it's safer than vaginal sex. That's probably also why we're seeing increases in these infections,” Leone said. “A lot of people don't think of their head and neck as a sex organ, which fuels the idea that we don't have to worry about acquiring an infection there.”
“The vast majority of infections will never lead to any sort of relevant disease, let alone cancer,” said Dr. Mark Einstein, head of the HPV Vaccine Clinic at Montefiore Medical Center in Bronx, N.Y. “Just because it's there doesn't mean it's doing anything or causing any cellular damage.”
Experts say the study provides another strong argument for vaccinating both boys and girls against HPV, a move recommended by the CDC in 2011. By 2008, only about 30 percent of women and even fewer men had gotten the vaccine, which has been approved for both men and women ages 9 to 26. HPV vaccines like Merck's Gardasil and Glaxo SmithKline's Cervarix have so far only been tested for their effectiveness against the virus that causes cervical, vulvar and anal cancer. The vaccines work against several strains of the virus, including HPV-16, which Gillison noted is responsible for about 90 percent of oral HPV cases, as opposed to about 57 percent of cervical HPV infections. “We have every reason to be optimistic that it will work against oral HPV, but we don't know directly because it's never been studied,” she said.