CHICAGO ? One in four U.S. women ages 14 to 59 is infected with the sexually transmitted virus that in some forms can cause cervical cancer, according to the first broad national estimate.

The figure is mostly in line with previous assessments. The highest prevalence ? nearly 45 percent ? was found in young women within the age range recommended for a new virus-fighting vaccine, according to a Centers for Disease Control and Prevention report.

Researchers have estimated that 20 million Americans have some form of HPV. The study concluded that 26.8 percent of U.S. women are infected, which is comparable to earlier estimates involving smaller groups.

"We expected the prevalence of any HPV infection would be high and that?s what we found," said CDC researcher Dr. Eileen Dunne, the study?s lead author.

Only 3.4 percent of the women studied were infected with one of the four HPV strains that the new vaccine protects against. But that doesn?t mean the vaccine should be written off, said Dr. Yvonne Collins, an assistant professor of gynecologic cancer at the University of Illinois at Chicago.

For one thing, Collins said, that relatively small percentage corresponds with a lot of women ? about 3 million, according to the report. And it does not include women whose infections have cleared up.
 

The number of women with HPV strains targeted by the vaccine was lower than in some previous, less-comprehensive estimates. And the prevalence of HPV among the youngest women studied, 14- to-24-yearolds, was substantially higher than in previous estimates, 7.5 million versus 4.6 million.

Dunne attributed those variations to different study populations and different HPV detection methods. The results don?t mean that infection prevalence has changed in recent years, she said.

The new report, which appears in today?s Journal of the American Medical Association, is based on vaginal swab specimens from 1,921 women tested from 2003 to 2004.

There are dozens of strains of HPV. Low-risk forms can cause genital warts and non-cancerous changes to cells in the cervix, and the strains often clear without treatment. Several high-risk forms have been linked with cervical cancer.

Dunne said HPV prevalence is thought to be high in men as well, but none was studied.

Cervical cancer will be diagnosed this year in an estimated 11,150 U.S. women, and about 3,670 will die from it.

The new vaccine, Merck?s Gardasil, was approved last June for girls and women aged 9 to 26. Other vaccines are in the works to protect against other HPV strains, Collins said.