Human papillomavirus infection: epidemiology and pathophysiology
More than 120 different types of the human papillomavirus (HPV) have been isolated; >40 of these types infect the epithelial lining of the anogenital tract and other mucosal areas. In the majority of individuals, HPV infections are transient and asymptomatic with most new infections resolving within 2 years. Epidemiological data from the U.S. National Health and Nutrition Examination Survey determined that the prevalence of HPV infection in a representative sample of women was highest in those aged 20-24 years (44.8%). HPV infection has been firmly established as the primary cause of cervical cancer. It is not clearly understood why HPV infections resolve in certain individuals and result in cervical intraepithelial neoplasias in others, but several factors are thought to play a role; including individual susceptibility, immune status and nutrition, endogenous and exogenous hormones, tobacco smoking, parity, co-infection with other sexually transmitted agents such as HIV, herpes simplex virus type 2 and Chlamydia trachomatis as well as viral characteristics such as HPV type, concomitant infection with other types, viral load, HPV variant and viral integration. Worldwide, pooled data from case-control studies indicated that HPV DNA could be detected in 99.7% of women with histologically confirmed squamous cell cervical cancer compared with 13.4% of control women. Both HPV infection and cervical cancer are associated with a substantial economic burden. Pharmacoeconomic data from the United States indicate that HPV infection and HIV were associated with similar total direct medical costs, and HPV infection was more costly than genital herpes and hepatitis B combined in the 15-25 age group. Furthermore, false-negative pap smears from women with precancerous lesions are among the most frequent reasons for medical malpractice litigation in the United States.