Human papillomavirus infection.

Human papillomavirus (HPV) is one of the most common sexually transmitted infections (STIs). More than 170 types of HPV have been classified and more than 40 types of HPV can infect the genital tract of humans.[1,2,3] Genital HPV types are divided into two groups based on whether they have an association with cancer. Infections with low-risk types (non-oncogenic) are not associated with cancer but can cause genital warts and benign or low-grade cervical cellular changes. Infections with high-risk types (oncogenic), most notably HPV types 16 and 18, can cause low-grade cervical cellular changes, high-grade cervical cellular changes (moderate to severe Pap test abnormalities), and cancer of the cervix; in addition, some high-risk HPV types have been associated with cancers of the vulva, vagina, anus, penis, and oropharynx.[4] Most HPV infections, whether caused by low-risk or high-risk types, are transient, asymptomatic, and have no clinical consequences. Estimates on the incidence and prevalence of HPV infection are limited because HPV infection is not a reportable infection in any state (genital warts are reportable in a select number of states). In addition, most HPV infections are asymptomatic or subclinical, and therefore not diagnosed. Available HPV-related data primarily focuses on the clinical sequelae of HPV infection, such as genital warts and genitourinary cancers.