Oral infections of human papillomavirus, or HPV, affect nearly 7% of Americans and are significantly more common in men than in women, according to a new Centers for Disease Control and Prevention study.
The study, which is the first to examine the prevalence of oral HPV in the U.S., found that three times as many men (10%) as women (3.6%) have HPV infections. The data may help to explain why the incidence of head and neck cancers has been increasing, particularly in males, even as smoking rates are on the decline.
For the study, CDC researchers plumbed data on 5,579 people aged 14 to 69 who participated in the National Health and Nutrition Examination Survey in 2009 and 2010. The participants answered extensive questionnaires about their sexual behavior and gave oral cell samples for analysis for HPV.
The researchers found that the risk of oral HPV infection increased with the number of sexual partners a person had: it was eight times higher in people who had ever had sex versus not, and as high as 20% in people who had had more than 20 sexual partners in their lifetime. The data indicate that “oral HPV infection is predominantly sexually transmitted,” through oral sex, not passed through casual contact like kissing, the authors concluded.
The CDC researchers also found that HPV infections peaked in two age groups: 30-to-34-year-olds, who had a 7.3% chance of infection, and 60-to-64-year-olds, who were 11.4% likely to be infected. It’s not clear why older people had higher rates of oral HPV, but the authors offered some possible theories: perhaps it’s because older people came of age at a time when there were fewer concerns about sexually transmitted infections, or perhaps latent HPV infections are becoming reactivated as the immune system weakens with age.
HPV is the most commonly sexually transmitted virus in the U.S. At least half of all sexually active people will acquire an infection at some point in their lives. Most will clear the virus on their own, but persistent infections can cause cancer, including cervical, vulvar, vaginal, anal and penile cancers. Oral infection with a high-risk strain of HPV can cause oropharyngeal cancers — cancers of the tonsils, upper throat and base of the tongue.
Rates of oral HPV infection are substantially lower than genital infections — which can be as high as 42% in women in their 20s, for example — but they are becoming increasingly troublesome. While HPV is best known as the virus that causes cervical cancer in women, because of better screening, the rate of such cancers has declined. Meanwhile, the rate of oral cancers is on the rise: a study published in October in the Journal of Clinical Oncology found that HPV-related oropharyngeal cancers increased 225% between 1984-89 and 2000-04. In 1984-89, about 16% of oropharyngeal cancers tested HPV-positive; by 2000-04, the proportion of HPV-positive cancers had risen to 72%, accounting for more oral cancer than smoking.
Overall, the risk was greatest and rising in men, the study found, possibly because of increasing rates of oral sex. The data indicate that the burden of HPV-related cancer may shift from women to men, with the number of HPV-positive oral cancers potentially eclipsing that of invasive cervical cancers within 10 years.
That supports efforts to boost HPV vaccination, suggest the authors of the current CDC study, published online by the Journal of the American Medical Association. Public health officials recommend that girls aged 11 or 12 be immunized with either of two approved HPV vaccines, Gardasil or Cervarix, which both protect against HPV 16 and 18, the strains that cause most cervical cancers. (Gardasil also protects against HPV strains 6 and 11, which cause 90% of genital warts cases.) Girls aged 13 to 26 should also be immunized if they haven’t been already.
The advice extends to boys as well, but only one of the shots, Gardasil, has been tested and approved for males to protect against warts and anal cancer. Boys are advised to receive the vaccine at age 11 or 12, or between ages 13 and 21 if they haven’t already been immunized. The primary reason for the advice is to protect adolescents and young adults from infection with the high-risk strains of cancer-causing HPV before they become sexually active.
It’s not clear whether the vaccines can also protect against oral cancers. More research is needed to figure that out. But researchers speculate that if the vaccine reduces rates of HPV in women, it can in turn help reduce the risk of infection in men.