WASHINGTON -- More than one-third of American women are infected with the human papillomavirus , which in rare cases can lead to cervical cancer, by the time they are 24 years old, according to a study being published today.
The new estimates suggest that there are 7.5 million girls and women ages 14 to 24 infected with the microbe -- 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 virus 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 that the findings don't mean 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 F. 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 the use of a vaccine against HPV approved in June by the Food and Drug Administration for females ages 9 to 26. Its maker,
In its just-completed session, Virginia's General Assembly passed legislation, now before the governor, requiring the vaccine for schoolgirls. Texas's governor last month issued an executive order doing the same thing.
"Our perspective is that many women would benefit from the protection that [the vaccine] would provide," said Richard Haupt, executive director for medical affairs at Merck Vaccines. The company is running studies trying to prove the vaccine's usefulness in boys and men aged 9 to 23.
Some parents have objected to school mandates for the HPV vaccination of girls, arguing that because the infection is transmitted only through sexual contact, it can be avoided by choice. Others argue that the vaccine may lower inhibitions against sexual activity, although there is no evidence that fear of HPV infection is a reason many teenagers abstain.
Cervical cancer was once the leading cause of cancer death for American women. Last year, there were about 9,700 new cases and 3,700 deaths. About 85 percent of the women who died had never had a Pap smear.