More than a quarter of teenage girls and women in the United States may have a common sexually transmitted virus. And most may not even know they have it.
A study published today in the Journal of the American Medical Association, which looked at nearly 2,000 women and girls aged 14 to 59 years, showed 27 percent overall were infected with one or more strains of human papillomavirus (HPV), making it the most common sexually transmitted disease (STD) in the United States.
The research also found that HPV is even more common in younger age groups, with nearly half of all women in their early 20s infected.
According to the study authors, "Our data indicate that the burden of prevalent HPV infection among women was higher than previous estimates."
Recent debate over proposed state programs mandating vaccinations with the HPV vaccine Gardasil for preteen girls has brought the virus into the national spotlight.
Public health experts say the move could protect many of these girls from cervical cancer, which can be caused by certain types of the virus. About 10,000 women in the United States are diagnosed with cervical cancer each year, and 3,700 women die from it.
Approximately 2 percent of women in the study were infected with one of the cancer-causing subtypes. Not all women who are infected with these subtypes will get cervical cancer, but the infection puts them at greater risk.
Many doctors say the findings are not shocking.
"We already knew this infection was common," says Dr. Kevin Ault, associate professor of gynecology and obstetrics at Emory University School of Medicine. "This just adds urgency to getting the vaccine to adolescents and young women."
Dr. Lisa Jones, a gynecologist in New Bedford, Mass., says she hopes the media coverage of HPV and its vaccine will help educate people about how widespread the virus is.
"It is not just 'bad girls' that get HPV," Jones says. "Even women with one partner in their lifetime are also at risk; all it takes is for their partner to have had one other partner."
But even though the findings were little surprise to doctors, they could come as a shock to the public.
"This is a more recent study, and it more accurately reflects what we're seeing in terms of sexual behavior," said Dr. Carol Brown of Memorial Sloan-Kettering Cancer Center in an interview with ABC medical correspondent John McKenzie.
And the figures could have the greatest implications for younger women. Researchers found that among females 14 to 24 years of age, 34 percent were infected with HPV. That suggests 7.5 million teens and young women infected nationwide -- much more than the 4.6 million in previous estimates.
"I think it's really shocking that the virus is so common," Brown told McKenzie.
"It horrifies me. I have a daughter, 18, and a daughter, 22."
Public health experts say information about the prevalence, or infection rate, of HPV is helpful at a time when young women are starting to be vaccinated against the disease.
In an editorial that accompanies the study, Susan Weller and Dr. Lawrence Stanberry of the Sealy Center for Vaccine Development in Galveston, Texas, say the study may provide a helpful baseline to later determine whether or not vaccination programs work.
Such findings may also help determine whether it is cost effective to vaccinate all young women, Weller and Stanberry say.