By Robert Preidt
The investigators also found that the risk for reinfection after a year increased 20-fold for men who've been infected with HPV16 -- the type responsible for most HPV-related cancers. And the risk was 14 times higher after two years.
This was true in both men who were sexually active and those who were celibate. That suggests that they are not re-acquiring the virus from another sexual partner, according to the study from the University of Chicago Medical Center.
The researchers analyzed data from more than 4,000 men who were not vaccinated against HPV. The men lived in Florida, Mexico and Brazil and were tracked from 2005 to 2009.
The findings show the importance of HPV vaccination in young males before they become sexually active, the study authors said.
"Vaccinating boys before HPV exposure could be a highly effective way to reduce the burden of HPV infection," study leader Sylvia Ranjeva said in a university news release. "Vaccinating men who have already been infected might also be effective." Ranjeva is a Ph.D. student in the university's department of ecology and evolution.
HPV is the most common sexually transmitted infection. It's a major cause of genital warts and cancers of the cervix, vulva, vagina, penis, anus, mouth and throat. About 40 percent of women and 45 percent of men in the United States are infected with HPV.
Among women, virtually all cases of cervical cancer are caused by HPV, and just two HPV types, 16 and 18, are responsible for about 70 percent of all cases, according to the U.S. National Cancer Institute.
There are more than 200 HPV types. Vaccines protect against four to nine of the most common, disease-causing types, the study authors noted.
The new report was published online Dec. 5 in the Proceedings of the National Academy of Sciences.