By Stephanie Stahl

PHILADELPHIA (CBS) — Sixteen million Americans—or seven percent—have oral human papillomavirus (HPV), a sexually transmitted virus that can cause cancer, according to a first of its kind study published by the American Medical Association.

READ MORE: Pennsylvania Gov. Wolf Calls On Lawmakers To Pass Fairness Act, Preventing Discrimination Based On Sexual Orientation, Gender

The numbers are surprisingly high, and doctors say the trouble is that most people don’t know they have it because there are no symptoms, which could be why HPV appears to be spreading so quickly.

“The title I’ve put on it is ‘Hazard of Intimacy,’” said Dr. Hans Schlecht, an infectious disease specialist at Drexel University College of Medicine, who wrote an editorial on the new research. He says the oral HPV virus can be caused by smoking and drinking, but it’s more commonly linked to sexual activity, especially among younger people.

“The behaviors of oral sex and deep kissing go together, so it’s difficult to tease out what gave that person oral HPV, whether it was an oral kissing episode or an oral sex episode,” said Dr. Schlecht.

And there’s no way to know if you have the oral HPV virus. There are no symptoms, so it’s easily spread.

“We’re talking about millions of people, ultimately,” said Dr. Schlecht.

READ MORE: Open For Business: Manayunk Chambers Guest House In Manayunk Can Be Anyone's Home Sweet Home

He also says there are many types of HPV; one is linked to oral cancer in men and women and to cervical cancer in women. But there is an HPV vaccine, which should be given to teenagers before they become sexually active in order to be most effective. However, it’s unclear if the vaccine will guard against oral HPV, though many researchers think it will.

In addition to the HPV vaccine, doctors say condoms can also help guard against the virus. Experts hope this new research will lead to the development of an approved screening for oral HPV.

Oral HPV Study Information

HPV Associated Cancer Information

Oral Cancer Information

MORE NEWS: Former Philadelphia City Council President Anna Verna, 90, Dies

HPV Vaccine Information

Stephanie Stahl