A new study released Tuesday said tobacco products up the risk of contracting a sexually transmitted virus linked to mouth and throat cancer.
Oral human papillomavirus type 16, or HPV16, is found in 80 percent of throat cancers and is transmitted by oral sex. Tumors related to the virus have increased by 225 percent in the United States in the past two decades.
"The practice of oral sex is common, but this cancer is rare," said Gypsyamber D'Souza, epidemiology professor at Baltimore's Johns Hopkins Bloomberg School of Public Health.
"There must be cofactors in the process that explain why some people develop persistent HPV16 infections and HPV-positive oropharyngeal cancers when most other people don't."
Researchers found that HPV16 infections are more common among people who smoke or use tobacco products, regardless of their sexual practices, though non-smokers are also at risk, according to the study in the Journal of the American Medical Association.
"It appears that tobacco exposure increases the likelihood of having oral HPV16 infection, and although we do not yet know why, we suspect that the virus may not be cleared from the body as easily in people who use tobacco," D'Souza said.
The study examined data from 6,887 participants from the National Health and Nutrition Examination Survey in the United States.
Among the group, 2,012 participants smoked or used tobacco products at the time of the study.
Researchers detected the virus in participants by administering a mouth wash that collected mouth and throat cells.
Participants' blood and urine samples were tested for chemicals related to tobacco usage, namely cotinine and NNAL, a tobaccorelated carcinogenic metabolite.
Subjects with elevated levels of tobacco-related chemicals in their blood or urine had a higher risk of having HPV16 DNA, while those without detectable traces of the biomarkers showed lower traces of the virus, the study said.
Among those with cotinine levels in the blood equivalent to smoking three cigarettes a day, the risk of HPV16 infection increased by 31 percent.
For participants with NNAL levels in their urine equal to smoking four cigarettes in a day, the likelihood of infection climbed 68 percent.
"These results may provide an additional reason for smoking cessation and suggest that even modest amounts of tobacco use are associated with higher oral HPV prevalence," co-author Carole Fakhry said.