March 7, 2007

Study Indicates HPV Infects 26.8% of Women

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Last week, the Journal of the American Medical Association published a study that determined the prevalence of the Human Papillomavirus among females in the United States. Among the 1921 participants ages 14 to 59, the study found a 26.8 percent prevalence rate of HPV. The study concluded that prevalence is highest among the 20 to 24-year-old age group, with a rate of 44.8 percent.

The study also differentiated between high and low-risk strains of the virus and looked at risk factors including age, race and number of sexual partners.

Liz Franzek ’08, president of the Sexual Health Awareness Group, said that these latest figures did not come as a surprise.

“The Center for Disease Control estimates that 50 percent of the population will get HPV at some point, although the 26.8 percent prevalence statistic did seem pretty high,” she said.

The study stated that 90 percent of HPV infections will clear themselves within two years. However, certain high-risk strains of the virus can cause pre-cancerous lesions of the cervix, which may lead to cervical cancer. Cervical cancer is the second leading cause of cancer deaths among women worldwide, and in the United States approximately 3,700 women die from the disease each year. Other strains of HPV can cause genital warts.

There are about 40 strains of HPV that affect humans, and about 12 of these are considered high-risk.

Last June, the FDA approved Gardasil, a vaccine that protects against the two most common cancer-causing strains of HPV as well as the two most common strains which cause genital warts. The shot, administered in three doses over a six-month period, has “demonstrated close to 100 percent efficacy in preventing infection and disease” among females without previous exposure, according to the study.

The shot is intended for females ages nine to 26, but is most effective in females who have not previously been in contact with any of the four strains in the vaccine. However, it is still effective in females who have been exposed because it is unlikely that anyone would carry all four strains.

Dr. Alexandra Hall of Gannett Health Services said that the study was particularly useful as a baseline for future studies to test the efficacy of the Gardasil vaccine.

Although the study found only a 3.4 percent prevalence rate of the strains associated with Gardasil among participants, Dr. Hall said that the shot is still worthwhile because approximately 20 percent of women will be infected with at least one high-risk strain in the vaccine at some point in their lives.

Dr. Hall also acknowledged some possible shortcomings of the study. “It looked at prevalence, which means that it focused on one slice in time,” she said. “It didn’t follow these women over a period of time, so it did not include infections which had already cleared naturally by a woman’s body or those still to come.”

She added that the methodology, a cervical swab which participants collected themselves-was probably less than accurate “because the cervix can be hard place to reach” and not all women may have performed the procedure correctly.

“Based on methodology alone,” said Dr. Hall, “the study probably underestimates the prevalence of HPV in the female population.”

Because most strains of HPV are asymptomatic and clear up on their own, most people will not ever know if they have been infected. However the virus becomes a problem when it causes genital warts or an abnormal Pap smear — an indicator of abnormal cell growth on the cervix. While no treatment options exist for the HPV infection, treatment is available for the conditions caused by the infection.

“The most important thing we tell female patients is to get regular, yearly Pap smears,” Dr. Hall said.

She noted that about 5 percent of Pap smears performed at Gannett come back abnormal due to HPV infection, which corresponds with the figures in the study.

Franzek agreed, stating that “for girls, getting a yearly Pap smear immediately decreases your risk of cervical cancer.” She added that both men and women should do periodical check-ins with their physicians to keep up with their own sexual health.

While the Gardasil vaccine protects for specific strains of HPV, there is no method 100 percent effective in preventing its spread.

“Condoms are helpful in protecting against certain strains which affect the cervix,” said Dr. Hall, “but they are not necessarily effective in preventing genital warts, which can be spread through skin to skin contact.”

There is no equivalent swab method to test for HPV in men, and, consequently, the vast majority of HPV research focuses on women. However, men can carry the virus unknowingly and readily transmit it to others. Researchers are testing the efficacy of the Gardasil vaccine in men, but this testing is still in an early stage.