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Millions of US Women Infected with HPV

Infections with human papillomavirus, or HPV, are more common among US women than previously suspected, according to new estimates from the US Centers for Disease Control and Prevention (CDC).

Nearly 25 million women ages 14-59 are likely infected with some form of HPV, the agency reports. Of those, more than 3 million are thought to have one of the 4 strains known to cause most cases of cervical cancer and genital warts. These are the same strains targeted by the recently approved vaccine Gardasil.

Gardasil was approved in June 2006. Federal vaccine officials recommended it be given routinely to girls at age 11 or 12, and said it could be given to girls as young as age 9 under certain circumstances. The American Cancer Society recently issued similar recommendations.

Vaccinating girls at this young age will help make sure they are protected against this very common sexually transmitted virus before they become sexually active, say health officials. The vaccine isn't likely to be as effective in people who have already been infected with one of the strains it targets.

The new estimates of HPV infections give researchers a baseline to measure just how effective the vaccine and the vaccination strategy are, the CDC researchers say. Infections Decline With Age

The numbers were pulled from the National Health and Nutrition Examination Survey (NHANES) 2003-2004, a yearly study of US health conducted through interviews and medical exams. More than 2,000 women and girls who were taking part provided a vaginal swab, which was tested for HPV. The researchers used infections in the participants to estimate how many women in the general US population are infected.

HPV infection was most common among 20-24-year-olds; nearly 45% had some strain of the virus (the researchers tested for about 43 strains that can be found in the genital region). About 25% of girls 14-19 were infected. Those figures included some who said they were not sexually active. When the researchers looked only at women who said they were sexually active, nearly 50% of 20-24-year olds and 40% of 14-19-year-olds had some type of HPV infection.

Estimates of infection in those 2 age groups were higher than ones from previous surveys and studies, the researchers say. HPV infections became less common as women aged; fewer than 20% of women in their 50s were infected.

Most of the women had types of HPV that are not considered high-risk -- that is, they are not known to cause cervical cancer. Overall, about 2% of women were infected with HPV types 16 or 18 -- the types most strongly linked to cancer.

Not every woman who has one of these HPV types will develop cancer, however. In most cases, the body is able to clear the infection before it ever causes any problems. Screening with Pap tests is the best way to catch dangerous changes in the cervix before they become cancer.

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