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Papillomaviruses are small viruses that infect tissues of the skin and mucous membranes. Human papillomavirus (HPV) is the most common sexually transmitted infection in the United States, affecting an estimated 75% of the U.S. population. More than 100 types of HPV have been identified, of which more that 40 are capable of infecting the genital tissues. In the U.S., it is estimated that over 6 million people are infected with genital HPV annually. Almost half of the infections are in persons aged 15-25 years. Sexual activity is the most important risk factor for infection, with 64% to 82% of sexually active adolescent girls testing positive for HPV. However, most HPV infections go undetected as they often cause no symptoms.

Anogenital warts are benign growths that often recur within the first 6 months of initial diagnosis and, therefore, require repeated treatment. Over 500,000 new cases of anogenital warts are diagnosed annually in the U.S. Approximately 10% of men and women will develop anogenital warts at some point in their lives. Current estimates suggest that >1% of the sexually active population has genital warts.

HPV infection is the cause of genital warts as well as most pre-invasive and invasive cancers of the genitals. Virtually all cancers of the cervix are thought to be caused by infections with HPV.

Genital HPV types have been separated into high and low risk groups depending upon the risk of progression to malignancy. HPV has been linked to several anal, penile, scrotal vulvar, vaginal and some head and neck cancers. The majority of HPV-associated disease is caused by 4 HPV types: HPV 6 and 11 are responsible for low-grade genital lesions and more than 90% of genital warts, and HPV 16 and 18 both account for approximately 70% of all high-grade CIN or dysplasia (abnormal cells) and invasive cervical cancer.

High risk HPV types are responsible for most high grade, precancerous lesions and >99.7% of cervical cancers. HPV 16 alone is the cause of more than half of all invasive cancers. It has been shown that HPV 16 and HPV 18 are cumulatively responsible for over 70% of all cervical cancers and the majority of precancerous neoplasia commonly detected during routine cervical cancer screening.

Most HPV infections are transient and infected women clear their infections within 1 year. Once negative for HPV, women are at greatly reduced risk for the development of dysplasia. However, a small fraction of women go on to develop persistent infection and are at risk for malignancy. The development of cervical cancer takes an average of 20 years.

Many women will become infected with high risk HPV types, however, even without any intervention, only 2% will develop precancerous lesions that might progress to cancer. Persistent infection with high risk HPV types is a major determinant for developing high grade pre-invasive cervical lesions. Persistent infection has been defined as detection of HPV DNA of the same HPV type in 2 or more consecutive tests at least 6 months apart.