1 in 4 U.S. Women Carries Cervical Cancer Virus

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The findings are published in the Feb. 28 issue of the Journal of the American Medical Association.

Because the body's immune system usually clears HPV from the body within six months, the study results do not reflect a woman's lifetime risk of ever acquiring the virus, the researchers stressed.

"People acquire these infections and then clear them," explained the study's senior author, Dr. Lauri Markowitz, another CDC medical epidemiologist who is director of the agency's HPV Vaccine Working Group.

In other words, a woman might pick up one strain of HPV through sexual contact in her teen years, then eliminate it, only to catch another strain later in life.

"So, this study was just a cross-section [of prevalence] at a point in time," Markowitz explained. "It doesn't explain your lifetime risk."

The study, which drew on data from the U.S. National Health and Nutrition Examination Survey (NHANES) for the years 2003-2004, also found that 3.4 percent of women aged 14 to 59 were infected with one of the four HPV strains covered by the Gardasil vaccine -- strains 6, 11, 16 and 18. Strains 16 and 18, especially, are suspected of being especially "oncogenic" (cancer-causing), experts say.

While 3.4 percent may not seem like a large number, Markowitz stressed that, again, this figure is reflective of a "point in time" and does not demonstrate a woman's lifetime risk of picking up these particularly dangerous strains. "So, this doesn't change our thinking about our [vaccine] recommendations," she said. "It substantiates the evidence that is already out there."

Another expert agreed that the new statistics support the widespread vaccination of young girls against HPV. However, efforts to do so have met with opposition from conservative groups and some parents, who worry that vaccination might encourage premarital sexual activity.

"That's more of a political question, of course," said Dr. Jennifer Wu, an obstetrician/gynecologist at Lenox Hill Hospital in New York City. "One thing that we do need to think about, however, is that we already vaccinate [girls] against hepatitis B -- it's a universal vaccine for children. And hepatitis B is also a sexually transmitted disease."