By SHELLY HOLMSTROM, M.D., Tampa Tribune, July 31, 2008

The human papillomavirus, known as HPV, is the most common sexually transmitted infection in the United States - and a leading cause of cervical cancer. The Food and Drug Administration's 2006 approval of the first vaccine against HPV, Gardasil, has promoted much discussion about the virus and its prevention.

The Centers for Disease Control and Prevention estimate that 20 million American women and men are infected with the HPV virus, which is passed through genital contact, most often during vaginal and anal sex. Nearly three-quarters of the new cases each year occur in 15- to 24-year-olds. Moreover, researchers estimate that 80 percent of sexually active women in the United States will have acquired genital HPV by the time they are 50 years old.

Fortunately, most people with an HPV infection will clear the virus from their body over time. If people smoke cigarettes, however, their immune systems are much less likely to fight off the virus.

Many genital tract infections with HPV are subclinical, meaning the person does not show symptoms or health problems. However, some low-risk HPV types cause genital warts. Other high-risk strains promote cell changes that may lead to cervical cancer and less common cancers, such as cancers of the vulva, vagina, anus and penis. These high-risk strains can be detected by a Pap test, a screening test for cervical cancer. Simply being diagnosed with a high-risk strain of HPV does not mean a woman will develop cervical cancer. She does need to follow up with her physician, however, for more frequent surveillance of the virus and treatment of any early signs of cervical cancer.

Risk factors for HPV include initiating sexual intercourse at a young age, having many sexual partners, and having a partner with a history of many sexual partners. Men and women can reduce their risk of HPV by using protection (condoms) and limiting the number of sexual partners.

The vaccine Gardasil, available for girls and women ages 9 to 26, protects against the four types of HPV that cause most cervical cancers and genital warts. This vaccine is given in three doses over six months. The series costs about $375, and most large insurance plans usually cover recommended vaccines. Gardasil is most effective in females who are not yet sexually active, since they are unlikely to have been exposed to HPV.

Women diagnosed with HPV infections (genital warts or abnormal Pap tests) can still benefit from the vaccine but probably will not receive full protection. Once a woman is vaccinated, she should still undergo regular Pap tests as advised by her physician, because the vaccine does not protect against all cervical cancers (about 30 percent are not covered by Gardasil).

A second HPV vaccine (Cervarix) that protects against HPV associated with cervical cancer is expected to be approved soon. Although no vaccine is licensed to prevent HPV-related diseases in boys and men, studies are being conducted to determine whether Gardasil is safe and effective for them. Over time, widespread vaccination could help prevent transmission of HPV in the population.

Dr. Holmstrom is an assistant professor in the Department of Obstetrics and Gynecology at USF Health.