TUESDAY, March 1 (HealthDay News) -- A new international study finds that half of adult males in the United States and elsewhere may be infected with human papillomavirus (HPV), a sexually transmissible virus linked to cervical cancer and other tumors.

The finding could help public health experts determine the value of widespread HPV vaccination of males, the study authors say.

"The incidence of genital HPV infection in men was high and relatively constant across age groups in Brazil, Mexico and the U.S.A.," concluded Anna R. Giuliano, of the H. Lee Moffitt Cancer Center and Research Institute in Tampa, Fla., and colleagues. "The results from this study provide much needed data about the incidence and clearance of HPV infection in men."

The study, which was funded by the U.S. National Cancer Institute and published in the March 1 online edition of The Lancet, also found that having multiple female or male sex partners greatly increased a man's risk of HPV infection and that, each year, about 6 percent of men are newly infected with HPV16, the virus that causes cervical cancer in women and also causes cancers in men.

In 2009, about 32,000 cases of cancers in American women and men were attributable to HPV infection, according to background information in the study. These included cancers of the cervix, vagina, vulva, penis, oral cavity, anal canal, and head and neck.

The study included 1,159 men aged 18 to 70 (mean age 32) in the United States, Brazil and Mexico. None of the men had HIV and they had no history of cancer. They were assessed every six months for an average of two years.

The risk of cancer-causing HPV infection was 2.4 times higher for men who had had 50 or more female partners, compared to men with one or no partners. The risk was 2.6 times higher for men who had at least three male anal sex partners, compared to men with no recent partners.

Exerts note that, in most cases, HPV infection is cleared away naturally by the body's immune system. However, viral clearance times can vary. The median duration of an HPV infection among men in the study was 7.5 months for any HPV and 12 months for HPV16, the strain known to be a major cause of cervical cancer.

There was no association between age and incidence of any HPV types, including those that cause cancer. But the researchers did find that the ability of the immune system to clear HPV infections increased with age.

In recent years, HPV vaccination in teen girls and young women has become widespread. But HPV vaccination remains uncommon in males, even though HPV is easily transmitted from men to women and greatly affects women's risk of disease.

The cost-benefit ratio of vaccinating men against HPV in order to protect women has not been definitively established, Dr. Joseph Monsonego, of the Institute of the Cervix in Paris, France, noted in an editorial accompanying the study.

"However, as more diseases are prevented through male vaccination, notably anal cancer, the greater the cost-effectiveness of routine vaccination of both sexes. Although we will continue to encourage protective measures, condom use and safe sex practices are of little value in clinical practice, with prevention of HPV transmission and its consequences still unconfirmed. HPV vaccination of men will protect not only them but will also have implications for their sexual partner," he wrote.

More information

The U.S. Centers for Disease Control and Prevention has more about HPV.