About one in 15 Americans is infected with oral human papillomavirus, a sexually transmitted virus that causes throat cancers, and the disease is especially common among men, new research shows.
The research is the first major study to document the nationwide prevalence of oral human papillomavirus, or HPV, a disease that has drawn growing attention from public health experts because it has fueled a rise in oropharyngeal cancers affecting the back of the tongue and the throat. Researchers showed last year that throat cancers caused by a particular strain of the virus, HPV Type 16, have tripled in the last 20 years. But it was unclear exactly how many people over all were carrying HPV, which exists in more than 40 forms.
By looking at thousands of people across the country, the authors of the new report found that 6.9 percent of adults and teenagers are infected with oral HPV of any kind. The virus was about three times as common in men as it was in women. And the scientists identified several behaviors that significantly raised the risk of becoming infected: increasing age, greater sexual activity and smoking cigarettes.
But the study, which was published in The Journal of the American Medical Association, also revealed some reassuring findings, said Dr. Maura L. Gillison, the chairwoman of cancer research at Ohio State University and senior author of the paper. While the overall prevalence of HPV was about 7 percent, only 1 percent, or roughly two million people, were infected with HPV 16, the strain linked to throat cancers and many cases of cervical cancer. Fewer than 10,000 cases of throat cancer caused by HPV 16 are diagnosed every year, indicating that most people with the virus do not develop cancer.
HPV is far more commonly found in the genital area, affecting up to 80 percent of men and women at some point in their lives. It is transmitted to the mouth area by intimate contact, including oral sex. Although no specific treatment exists for the disease, in most people the immune system can fight off the infection. But, in a small percentage of cases, the virus can cause genital warts or lead to cancer, including cervical, vaginal and vulvar cancers in women and anal and oral cancers in men and women.
Two vaccines have been the focus of the prevention of HPV. Health officials recommend vaccination only for girls, as a way to prevent cervical cancer. But last year a federal advisory committee recommended expanding routine use of the vaccine to adolescent boys and men at high risk. The finding that oral HPV infections strike men more frequently than women may lend more weight to that recommendation.
“I think pediatricians might find that helpful information in talking about vaccination with the parents of boys,” Dr. Gillison said. “I think there’s a lot of information here that can further stimulate research into prevention.”
As part of the new study, nearly 6,000 people across the country — men and women ages 14 to 69 — were tested at mobile examination centers. Researchers took oral samples from the subjects, then used DNA testing to identify the HPV types they carried. They also asked detailed questions about their lifestyles, drug and alcohol use and sexual behaviors.
Over all, 10.1 percent of men were infected orally with HPV of one type or another, compared with 3.6 percent of women. The reason for the higher rate among men was unclear. The men in the study tended to have higher numbers of sexual partners than the women, but statistical analyses showed that this accounted for 16 percent of the difference in virus prevalence. One line of speculation was that hormonal differences in women might play a protective role, or that oral sex on women for some reason causes a greater likelihood of transmission.
But either way, the finding that men had triple the rate of infection dovetailed with earlier research on HPV-related throat cancers, which are about three times as common in men as they are in women, a difference that until now had not been explained. Some experts suspected that HPV rates for men and women were similar, but that HPV was simply more virulent in men.
By looking at the effects of various behaviors on infection rates, the study showed that a greater number of lifetime sexual partners as well as sexual activity of any kind — vaginal, anal or oral sex — heightened the risk. The disease also becomes more common with increasing age.
But sex was not the only behavior that heightened the odds of contracting HPV: cigarette smoking was an independent risk factor as well. Plenty of research shows that smoking can weaken the immune system, which may make people more susceptible to infection, Dr. Gillison said. Smoking may also make transmission more likely by damaging the lining of the mouth.
“I didn’t really anticipate smoking being so strong and so clearly independent of sexual behavior as a risk factor,” she said. “There might be something about smoking that’s changing the susceptibility of the epithelium to infection.”