Even girls who have not had sexual intercourse are at risk for infection with human papillomavirus (HPV), a new study shows.

In the study, which involved teen girls and young women, 11.6 percent of those who had never had sexual intercourse were infected with at least one strain of HPV.

HPV is a sexually transmitted disease that is most commonly passed between people during vaginal or anal intercourse. But it can also be transmitted through genital-to-genital, or hand-to-genital contact, which is how the participants in the study likely got the virus, the researchers said. Out of the more than 40 sexually transmitted HPV strains, more than a dozen have been identified as cancer-causing, according to the National Cancer Institute.

HPV infections are usually transient, but can cause cervical cancer in some people if the infection lingers for long periods.

The findings support the recommendation to administer the HPV vaccine to girls ages 11 and 12, before many become sexually active, the researchers said. Doctors and parents should not delay HPV vaccination because a teen is not sexually active, they said.

"Even before kids have intercourse,they're being exposed to HPV," said study researcher Lea Widdice, an assistant professor of pediatrics at Cincinnati Children's Hospital. "Vaccination at 11 to 12 years old is not too early," Widdice said.

Because the study was conducted in just one community of mainly African American young women, further research is needed to see if the findings apply to the general population. A high percentage of the participants in the study had become sexually active or had sexual contact, and the prevalence of HPV may be lower in a group with different sexual behaviors, experts say.

One of Widdice's teammates receives funding from Merck, the company that manufactures the HPV vaccine Gardasil.

Widdice and colleagues analyzed information from 259 girls ages 13 to 21 who visited a clinic in Cincinnati and got their first HPV vaccination between 2008 and 2010. The majority of participants (78 percent) were African American, and 75 percent reported having public health insurance.

Participants were asked whether they had ever had sexual intercourse, or whether they had ever had sexual contact without intercourse. A swab was used to collected cell samples from the vagina and cervix (either by doctors or the participants themselves), and the samples were tested for HPV.

One hundred ninety participants (73 percent) were sexually experienced, and many had had multiple sexual partners; the average number of sexual partners was about six. Among sexually active participants, 133 (70 percent) tested positive for HPV.

Of the 69 participants who had not had sex, eight tested positive for HPV, two of whom had HPV-16, a high-risk type of HPV. (Most cervical cancers are caused by HPV-16 or HPV-18.)

Eduardo Franco, a cancer epidemiologist at McGill University, in Montreal, said the percentage of girls in the study who tested positive for HPV and had not had sex was higher than he would have expected. But this may be because many of the girls in the group had had some type of sexual exposure, said Franco, who was not involved in the study.

It's not clear whether the HPV infections seen in this study were found in the vagina or in the cervix, Franco said. HPV infections in the cervix are more risky in terms of their cancer-causing ability, but would be less likely in those who have not had sexual intercourse, Franco said.

The vaccines currently available prevent both vaginal and cervical strains, though they must be given before the infection emerges. That said, women who have an HPV infection in the vagina would still be protected against the cervical kind if they then get the HPV vaccine, Franco said.

(Gardasil protects four strains of HPV, while the vaccine Cervarix, manufactured by GlaxoSmithKline, protects against two strains.)

Widdice and her colleagues detail their results in the August issue of the journal Archives of Pediatric & Adolescent Medicine.