Human papillomavirus: epidemiology and public health.

Approximately 15 types of human papillomavirus (HPV) infection cause virtually all cases of cervical cancer. Human papillomavirus 16 is the major type, accounting for approximately 50% of cases. The major steps of cervical carcinogenesis include HPV infection, viral persistence and progression to precancer (as opposed to viral clearance), and invasion. Human papillomavirus is the most common sexually transmitted infection. However, most HPV infections become undetectable by even sensitive HPV DNA testing within 1 to 2 years. The prevalence of infection peaks at young ages and declines thereafter, perhaps as the result of HPV type-specific acquired immunity. Most HPV infections are neither microscopically evident nor visible, making HPV DNA detection the diagnostic reference standard. Poorly defined immunologic factors are the major determinants of viral outcome. Smoking, multiparity, and long-term oral contraceptive use increase the risk of persistence and progression. Other sexually transmitted infections (eg, Chlamydia trachomatis), chronic inflammation, and nutritional factors might also play a role. Overt, long-term viral persistence in the absence of precancer is uncommon. New prevention strategies can be derived from the evolving knowledge of HPV carcinogenesis. Human papillomavirus vaccination is the ultimate prevention strategy, and large-scale trials are already underway. In the meantime, HPV DNA diagnostics are more sensitive although less specific than cytology, permitting a consideration of lengthened screening intervals. In terms of public health education, clinicians and patients will need to shift discussions of the mildly abnormal Papanicolaou test to consideration of HPV infection as a common sexually transmitted infection that rarely causes cervical cancer.