1 in 4 women in U.S. has HPV, study says

WASHINGTON — More than one-third of American women are infected by human papilloma virus (HPV), which in rare cases can lead to cervical cancer, by the time they are 24 years old, according to a study published today.

The new estimates suggest that there are 7.5 million girls and women aged 14 to 24 infected with the virus — about two-thirds more than an earlier but less broad-based study had found.

Overall, about one-quarter of women under age 60 are infected at any given time, making HPV by far the most common sexually transmitted disease in the country.

News of the higher-than-expected prevalence of HPV infection was balanced by the discovery that only 2.2 percent of women were carrying one of the two virus strains most likely to lead to cervical cancer — about half the rate found in previous surveys.

The lead researcher cautioned the findings don't mean that HPV infection rates are rising, only that they are higher than thought.

"For us, it's just a different measurement, and a more accurate one," said Eileen Dunne, a physician and epidemiologist at the Centers for Disease Control and Prevention.

The estimate comes from the federal government's ongoing National Health and Nutrition Examination Survey, which provides the clearest snapshot of the American population's health through dozens of measurements, laboratory tests and survey questions.

The new findings, published in the Journal of the American Medical Association, are likely to further encourage use of a vaccine against HPV approved in June by the Food and Drug Administration for females aged 9 to 26. Its maker, Merck & Co., until recently was lobbying state legislatures to mandate vaccination of middle-school girls, a step that more than 18 states are moving toward.

Some parents have objected to mandates for HPV vaccination of girls, arguing that because the infection is transmitted only through sexual contact, it can be avoided by choice.

There are dozens of strains of HPV, but only some can lead to cancer. Two — HPV-16 and HPV-18 — are responsible for about 70 percent of cervical cancers worldwide. The Merck vaccine protects against both, as well as two other strains that cause genital warts.

Most of the time a woman's immune system clears the virus within weeks, although repeated reinfections are possible. In some cases, however, the virus becomes incorporated in cervical cells and can cause malignant changes.

Cervical cancer was once the leading cause of cancer death in American women. Routine screening with Pap smears has reduced deaths dramatically in the past three decades. Last year, there were about 9,700 new cases of cervical cancer in the United States and 3,700 deaths. About 85 percent of the women who died had never had a Pap smear.

In the 2003-04 round of the national health survey, about 2,000 females aged 14 to 59 submitted self-collected vaginal swabs. Laboratory testing detected HPV in 27 percent of them. In the 14-to-24 age group, the rate was 34 percent. The highest prevalence — 45 percent — was in women ages 20 to 24.

HPV also infects boys and men, in whom it can cause genital warts and anal cancer. Males weren't tested in the survey, although researchers are trying to come up with ways to do that, Dunne said.