Infections with the human papillomavirus (HPV) in the mouth or throat are not common, but a new study finds that about three-quarters of women who do have an oral HPV infection also have a vaginal HPV infection.

The study also found that women who'd had two or more oral sex partners in the past year were three times more likely to have both oral and vaginal infections with the same strain of HPV (called a concordant infection) than women who'd had no oral sex partners in the past year.

The findings support the "genital-oral transmission theory," the researchers said, in which an HPV infection of the genitals is transmitted to the mouth or throat through oral sex.

Doctors already screen for vaginal HPV infections when a woman has a pap smear, because the virus is linked with cervical cancer. Certain strains of HPV area also linked with oral cancers, but "currently, there is no 'throat Pap smear' for screening so, outside of research protocols, we don't know who has oral HPV infection," said study co-author Dr. Ryan Orosco, a chief resident of head and neck surgery at the University of California, San Diego.

The researchers hope the findings help guide the development of future oral and vaginal HPV screening recommendations

For example, the new findings suggest that women with oral HPV may merit closer screening for vaginal HPV, Orosco said.

"We hope that our study increases the awareness that HPV infection has implications for both vaginal and throat health," Orosco told Live Science. [10 Do's and Don'ts to Reduce Your Risk of Cancer]

Many HPV infections go away on their own, and the study was not able to look at the risk of developing either cervical or head and neck cancer in women with HPV infections. So it's too early to make official recommendations based on the findings, Orosco noted.

In the study, the researchers analyzed information from more than 3,400 U.S. women ages 18 to 69 who were tested for oral and vaginal HPV infections in 2014. The women were tested for 37 different strains of HPV, and only some of these are linked with cancer.

Nearly half (45 percent) of the women had a vaginal HPV infection, and 4 percent had an oral HPV infection. Three percent of the women had both an oral HPV infection and a vaginal HPV infection, and 1 percent had a concordant infection.

About 76 percent of the women with an oral HPV infection also had a vaginal HPV infection, and about 7 percent of the women with a vaginal HPV infection also had an oral HPV infection, the study found.

Women who had performed oral sex on a new partner in the past year were twice as likely to have a dual oral and vaginal HPV infection, compared with women who had not performed oral sex on a new partner in the past year. But women who'd had a new oral sex partner more than a year ago were not at increased risk for a dual infection, the study said.

A woman's total number of lifetime sexual partners was also not linked with her risk of having a dual oral and vaginal HPV infection.

The findings may help improve discussions between women and their doctors about sexual behavior and the risks of oral HPV infections, Dr. Jonathan M. Bock, an otolaryngologist (ear, nose and throat doctor) at the Medical College of Wisconsin, wrote in an editorial accompanying the study.

"Discussion of condom use or other barrier-method protection during sexual contact for otolaryngologic patients with known oral or cervical HPV is … of paramount importance," Bock said.

In addition, the findings suggest that there may be a benefit of screening partners, including screening for vaginal HPV in female partners of men with certain oral cancers, and HPV screening of the mouth and throat for partners of females with high-risk HPV vaginal infections, Bock said.

The new study also "endorses the role of physicians and otolaryngologists in advocating for HPV vaccine administration in all patients, both male and female," Bock said. The HPV vaccine prevents infection with the types of HPV strongly linked to cancer.

The current study did not find a link between being vaccinated against HPV and the risk of dual oral/vaginal HPV infection. But because most of the people who have received the HPV vaccine in the past decade have been teenagers, this study (of adult women) would not be expected to find an effect, the researchers said.

The study and editorial are published in the March 24 issue of the journal JAMA Otolaryngology–Head & Neck Surgery

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