HPV Incidence in University Women

About 40 of the more than 100 types of human papillomavirus (HPV) cause genital infections; 18 of these 40 were recently defined as being high risk types for cervical cancer (N Engl J Med. 2003; 348: 518-527).

To estimate what proportion of university women acquire HPV infections over time and to determine risk factors for viral acquisition, the authors of this article (Am J Epidemiol. 2003;157(3):218-226) solicited volunteers from 18- to 20-year-old female university students in the Pacific Northwest. About 20% (just over 600) of the women approached by mail over a 7-year period enrolled in the study. Women were interviewed regarding their sexual activity and had pelvic exams every four months. Cervical specimens were collected for HPV DNA (genetic material that provides the blueprint for the virus) testing at the time of the visit; self-collected oral specimens were also submitted for HPV DNA testing. If HPV was detected in any specimen, additional tests were performed to determine what specific type of HPV was present.

Almost one fifth (19.7%) of the women who volunteered were excluded from further follow up because they were infected with HPV at the time of their initial visit. More than 400 women (444) completed over 4,000 visits. Most women had about 10 visits, each about 4 months apart. One third of the women were virgins at the beginning of the study; of the two-thirds who had already initiated sexual activity, the average number of lifetime partners at study entry was 1.8.

Among the two-thirds of women who were negative for HPV but sexually active at study entry, just under 40% (38.8%) became infected with HPV within two years. About 40% of the women who were virgins at the beginning of the study who initiated sexual activity over the course of the study also acquired HPV within two years.

2.4% of the women who remained virgins acquired some type of HPV over a two-year period (generally not a high-risk HPV type). Any type (i.e., finger-genital, oral-genital) of nonpenetrative contact was associated with some, albeit small, risk for genital HPV acquisition. Only one woman who reported no type of genital contact tested positive for HPV. Only a few oral samples were positive for HPV DNA; there was no association between oral sex and HPV DNA in oral samples.

Risk factors for HPV acquisition included having known a partner less than 8 months before initiating sexual activity (odds ratio [OR] 1.8, 95% confidence intervals [95%CI] 1.2, 2.7), current smoking (OR 1.5, 95%CI 1.0, 2.3), and current use of oral contraceptives (OR 1.4, 95%CI 1.01, 1.8). "Always use" of condoms did not protect against HPV infection.

Genital human papillomavirus infection: incidence and risk factors in a cohort of female university students. Winer RL, Lee SK, Hughes JP, Adam DE, Kiviat NB, Koutsky LA. Am J Epidemiol: 2003;157(3):218-226.

Comment: The main drawback of this excellent study is the rather low participation rate (about 20%) among the university women who were approached. Women who thought it would be a good idea to participate (i.e., be tested for HPV every 4 months) might have been rather different from women who did not. In addition to highlighting that any sexually active woman who is HPV negative appears to have a 40% probability of becoming infected within two years, this study also points out that even nonpenetrative sexual activity carries a small but real risk of HPV infection.

Given that having sex with any new partner increased the risk of infection and that condom use was not protective, data from this study support the concept of "the fewer partners the better" to reduce the risk of HPV infection somewhat and lifetime abstinence or monogamy as the best and only way to prevent HPV infection and all its consequences (i.e., primary prevention).

Secondary prevention (i.e., detection and treatment of a majority of early cancers) is also possible for women who have become infected with HPV, and the Medical Institute encourages all women who have ever been sexually active to have annual Pap smears.

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