Chapter 52 Sexually Transmitted Infections: Human Papillomavirus
INTRODUCTION
Description: Infection by one or more subtypes (of the more than 100 known) of human papillomaviruses (HPV) causes epithelial proliferations at cutaneous and mucosal surfaces. Some serotypes are associated with warty growths on the hands, feet, and other locations (including genital warts). Some high-risk serotypes are found in more than 99% of cervical cancers.
Prevalence: Thought to be the most common sexually transmitted disease in the world. About 20 million people are currently infected with HPV. At least 50% of sexually active people acquire genital HPV infection at some point in their lives. One study estimated that 64% to 82% of adolescent girls were infected with at least one strain of HPV. By age 50, at least 80% of women will have acquired genital HPV infection. About 6.2 million Americans acquire a new genital HPV infection yearly.
ETIOLOGY AND PATHOGENESIS
Causes: Exposure to the DNA human papillomavirus. More than 40 serotypes are know to be sexually transmissible. Vertical transmission from mother to child during childbirth can occur and rarely results in laryngeal polyps (approximately 2/100,000 births). Papillomaviruses initiate infection in the basal layer of the epithelium, and viral genome amplification occurs in differentiating cells. After infection, differentiating epithelial cells that are normally nondividing remain in an active cell cycle. This can result in a thickened, sometimes exophytic, epithelial lesion. The virus is released as cells exfoliate from the epithelium. Research indicates that HPVs produce proteins (designated E5, E6, E7) that interfere with tumor suppressor p53 proteins that arrest the cell cycle when there is DNA damage.
Risk Factors: Direct contact with an infected individual; therefore, having multiple sexual partners or contact with a person with multiple sexual partners increases the risk. Viral persistence is more likely in those with reduced immunity and tobacco smokers. Other epidemiologic factors associated with risk of cervical cancer include long-term use of oral contraceptives, coinfections such as chlamydia, parity, and nutritional factors.
CLINICAL CHARACTERISTICS
Signs and Symptoms
• Most are asymptomatic and are cleared spontaneously (70% by 1 year and more than 90% within 2 years; median infection: 8 months)
• Persistent infections may be associated with warty growths at the site of infection (condyloma accuminata) and cellular changes associated with dysplasia or cancer (including cancers of the anus, vulva, vagina, cervix, and some cancers of the oropharynx).
The incubation period required before symptoms appear is highly variable and varies from several weeks to years.
DIAGNOSTIC APPROACH
Workup and Evaluation
Special Tests: HPV serotyping for those with abnormal cervical cytology (Pap tests), colposcopy for those with persistently abnormal cytology or for surveillance of those with high-risk serotypes.
Diagnostic Procedures: Serotyping of HPV obtained from cervical cells can be performed but is not indicated on a routine or screening basis. Generally, this testing is reserved for those with abnormal cervical cytology (ASCUS [atypical squamous cells of undetermined significance] or above Pap tests). These tests will identify 13 high-risk serotypes. (Because most younger patients will clear even high-risk serotypes with no sequela, recommendations for serotyping and aggressive follow-up of abnormal Pap test results are changing to more conservative management schemes.)
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