Oral HPV infections are much higher than expected among American adults, according to a new study of 5,500 people. Experts say the study also paints a picture of changing sexual practices in the U.S. and advances the case for expanding vaccination against the virus among children and young adults.
Nearly 7 percent of 14- to 69-year-olds in the U.S. have oral HPV, according to the report published today in the Journal of the American Medical Association. Men were at three times greater risk than women for infection with the virus, particularly from age 30 to 34 and 60 to 64.
About 1 percent of the population -- nearly 2 million people -- has HPV-16, a particular strain of the virus that has been linked to oral cancers. The study said that this strain of the virus puts a person at a 50-fold increased risk of developing oral cancer.
The study is the first to give an idea of just how common oral HPV is among Americans. Much more is known about the version of the virus that leads to cervical cancer, which has recently been publicized by the creation of a vaccine against it. But experts say oral HPV is still something of a mystery. Unlike for genital HPV, oral HPV has no approved screening test.
"We know almost nothing about oral HPV infections," said Dr. Maura Gillison, the study's lead author.
But the study gives new insight into the factors that make oral HPV infection more likely. Perhaps not surprisingly, one of those factors is sex. Less than 1 percent of people who had never had sex had oral HPV in the study, but the risk of infection for those with sexual experience was nearly eight times greater. The risk also edged higher as people reported greater numbers of sexual partners.
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."
Experts say studies show that more people are having oral sex at younger ages than in decades past. The Centers for Disease Control and Prevention reported that 48 percent of heterosexual males and 44 percent of heterosexual females ages 15 to 19 reported having oral sex in a 2008 survey.
Oral sex often does not get the same attention when it comes to protection as other intercourse. Condom sales in the U.S. have increased, but Leone said people most likely use them exclusively for vaginal or anal sex.
"In my experience, very, very few people use condoms or dental dams for oral sex," Leone said.
Smoking was also an important risk factor for oral HPV in the study, possibly indicating that it leaves the body more vulnerable to infection, particularly in the mouth and throat.
More oral sex with less protection may be one reason why the risk of oral HPV was so heavy for men, though the study didn't provide any official reason for the gender difference in infection. The authors speculated that the virus may have an easier time transmitting orally in men than in women, or that other factors like smoking that are more common among men could facilitate transmission.
The data are cause for alarm because of increasing rates of oral cancer, a portion of which are caused by the virus. HPV is best known for its connection to cervical cancer, which affects more than 12,000 women each year, according to the CDC. The agency reported that about 7,100 develop HPV-related throat cancers each year, but the study noted that if present trends continue, oral cancers may overtake cervical cancer as the leading source of HPV-related tumors by 2020.
In October, Gillison published a study showing that the number of HPV-related oral cancers shot up from 16 percent to 72 percent in a 20-year period.
But experts emphasize that the link between oral cancer and HPV is still scientifically shaky.
"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.
Dr. Hans Schlecht, an assistant professor of infectious diseases at Drexel University College of Medicine in Philadelphia, said it will probably take at least a decade to know whether the vaccines are effective against oral HPV.
"It does work in the genital area, but we don't know anything about the mouth yet," Schlecht said. "It makes sense, but right now it's just guesswork."
Experts say protection against oral HPV begins by practicing safe oral sex and quitting smoking.
Schlecht added that doctors should be increasingly vigilant about looking for signs of oral cancers in their patients, which can include earache, difficulties with speaking or swallowing, and lumps in the neck.