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Prevention of Genital Human Papillomavirus Infection
Report to Congress Page 2

Introduction
Human papillomaviruses (HPV) are members of the Papillomaviridae family of DNA viruses. Because HPV cannot be cultured easily in the laboratory, HPV infection is most commonly diagnosed by detecting HPV DNA. Differences in sequences of DNA are used to determine different HPV types. More than 100 HPV types have been identified, over 30 of which infect the genital area. Genital HPV infections are estimated to be the most common sexually transmitted infection in the United States, with an estimated 5.5 million persons becoming newly infected every year (1). Although the majority of infections cause no symptoms and are self-limited, genital HPV is of public health concern because persistent infection with certain types can cause cervical cancer in women.

Genital HPV infections are categorized according to their association with cervical cancer. Infections with low-risk types, primarily types 6 and 11, can cause benign or low-grade cervical cell changes and genital warts, but are not associated with cervical cancer. Infection with high-risk types, primarily types 16, 18, 31, and 45, can cause low-grade cervical cell abnormalities, high-grade cervical cell abnormalities that are precursors to cancer, and genital cancers. Most genital infections with either high-risk or low-risk HPV types go away on their own, without clinical consequences. Currently, one HPV DNA test is FDA-approved for use in women for cervical cancer screening; no HPV test is available for men.

The sequela of genital HPV infection with greatest public health importance is cervical cancer. Cervical cancer is relatively uncommon in the United States because widespread cervical Papanicolaou (Pap) testing can detect precancerous lesions before they develop into cancer. However, in many developing countries where cervical cancer screening activities are limited, cervical cancer is the most common cancer in women. Based on multiple lines of evidence, both the International Agency for Research on Cancer and the National Institutes of Health (NIH) have concluded that high-risk genital HPV infections act as carcinogens in the development of cervical cancer (2;3). While infection with high-risk types appears to be “necessary” for the development of cervical cancer, it is not “sufficient” because cancer does not develop in the vast majority of women with HPV infection (2;3). Other co-factors appear to be necessary for the development of cervical cancer (described in Natural History of Genital HPV Infection, page 10). HPV infection is also associated with anogenital cancers at other sites including the vulva, vagina, penis and anus. Each of these is substantially less common than cervical cancer, with the exception of anal cancer in homosexual men (4-8). The association of genital types of HPV with non-genital cancer is less well established, but studies support a possible role in a subset of head and neck (9) and esophageal (10) cancers. In each of these non-genital cancers, there are clearly cancers arising independent of HPV, a situation quite different from cancer of the cervix. While a few studies suggest a possible association of HPV with cancer of the prostate (11), the findings are not consistent and the most recent studies do not indicate that HPV is associated with these cancers (12;13).

Because of the public health importance of cervical cancer, this report focuses on the prevention of genital HPV infection and its sequelae in heterosexual men and women. The report describes key aspects of the epidemiology of genital HPV infection and its transmission, and summarizes the best strategies to prevent infections with genital HPV as well as the HPV-associated diseases of genital warts and cervical cancer.

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