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Article Excerpt
Abstract
Human papillomavirus (HPV) is a highly prevalent, sexually transmitted infection responsible for significant morbidity and mortality. High-risk HPV types are now known to be necessary in the etiology of cervical cancer and to lead to both high-grade and low-grade cervical lesions. They are also implicated in a substantial portion of anal, penile, and head and neck precancers and cancers. HPV 16 and 18 are the most common HPV types found in cervical cancer and are responsible for approximately 70% of these cancers. In contrast, low-risk HPV types, the most common of which are HPV 6 and 11, cause genital warts, low-grade cervical lesions, and recurrent respiratory papillomatosis, but they do not cause cervical or other HPV-related cancers. Infection is most common in young, sexually active populations, and an estimated three fourths of adults will be infected with HPV during their lifetime. Cervical screening programs exist in the United States and other developed countries to identify and treat precancerous cervical lesions, but they do not reach all women and are costly. Until recently, no highly effective primary prevention strategy to reduce the risk of HPV acquisition existed. However, a quadrivalent HPV vaccine, which protects against the most common high-risk and low-risk HPV infections (HPV 16, 18, 6, and 11), is now available. In addition, a bivalent HPV vaccine that protects against high-risk HPV types 16 and 18 is in the late stages of clinical development. If implemented widely, vaccination against HPV promises to dramatically reduce HPV-associated morbidity and mortality.
Epidemiology of HPV Infection
Human papillomavirus (HPV) is the most common newly acquired sexually transmitted infection (STI) in the United States, with more than 6.2 million new HPV infections estimated to occur each year. (1) Seventy-five percent of sexually active Americans will be infected with HPV at some point in their lives. (2) HPV infection is most likely to occur in youth: 74% of new infections occur in individuals 15 to 24 years of age, (1) and the highest incidence of HPV is consistently found in sexually active women younger than 25. (2)
More than 100 types of HPV have been discovered and are generally classified as high-risk or low-risk types on the basis of their oncogenicity. (3) Among the high-risk types, HPV 16 and 18 account for approximately 70% of all cases of cervical cancer. (4) High-risk HPV types are also associated with the majority of cases of anal, penile, vaginal, and vulvar cancers, (4,5) as well as with a proportion of head and neck cancers. (6-8) HPV types 6 and 11 are the most common low-risk types and are associated with more than 90% of cases of genital warts. (9) HPV types 6 and 11 are also responsible for a small proportion of low-grade cervical cell abnormalities and for the vast majority of recurrent respiratory papillomatosis (RRP), a rare, yet potentially life-threatening condition. (5, 10)
In a review of prevalence studies of adolescent and college-aged women repeatedly tested over time for HPV, as many as 90% tested positive for HPV at least 1 time. (11) Older women are also at risk: 34% of a sample of older, postmenopausal women (median age 56), most of whom had had only 1 sexual partner in their lifetime, were HPV-positive at some point during a 7-year follow-up, suggesting that the sexual history of the partner(s) may be a codeterminant of risk. (12)
Less is known about the prevalence and patterns of HPV infection in men. Studies have established the incidence of HPV infection in men at 4% to 45%, with low rates generally reflecting the absence of a sensitive HPV testing method for males. Higher rates of infection are generally found in studies with soldiers or visitors to STI clinics, or men in their twenties. Lower infection rates were found in the general population samples with a higher median age. (13) In the United States, the prevalence of HPV infection in men is estimated to be approximately 30%. (13) However, because HPV is a "shared" virus, it is most likely that HPV prevalence rates in men and women are identical and that differences likely reflect the difficulty in detecting the virus in men as compared with women. (13)
Transmission of HPV
HPV is spread primarily by sexual contact, the exception being RRP, which is most frequently spread perinatally from mother to child. (10) The incidence of HPV infection increases dramatically with the number of sexual partners (FIGURE 1). (14) Intromissive intercourse is not a prerequisite for HPV transmission, as women who remained virgins throughout a 2-year longitudinal study still had a 2-year cumulative HPV infection rate of 2.4%, and approximately 10% of virgins who engaged in nonpenetrative sexual contact (eg, finger-vulvar, penile-vulvar, oral-penile) were HPV-positive. (15)
Condoms do not completely...
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