Difficulties in estimating the male-to-female sexual transmissibility of human papillomavirus infection.

Estimates of transmissibility of infectious agents such as human papillomavirus (HPV) are important for developing preventive measures and determining the impact of such interventions. Based on the results of epidemiologic studies, HPV appears to be highly transmissible;1–8 however, empirical data on HPV transmissibility are lacking.9–11 We sought to design and conduct a study among couples to provide the first empirical estimate of male-to-female sexual transmissibility of HPV. However, we faced several difficulties in achieving this goal. Here we present the design and descriptive results of this study in brief and these difficulties in detail. Information on study population arose from a larger study described in detail elsewhere.5 Briefly, between December 2000 and November 2006, 244 women (age range: 18–22) were recruited to a longitudinal study of HPV infection through invitational letters mailed to 24,201 female University of Washington undergraduates and informational flyers at the student health clinic. Participants were eligible to enroll if they had never had vaginal intercourse with a male partner (i.e., virgin) or had first had intercourse with one male partner within the previous three months (i.e., peri-virgin). Consenting women were asked to refer their first male partner to the study and were given a letter of recruitment to forward to him. Every two weeks, women completed a Web-based diary designed to capture daily sexual behavior information such as date and number of acts of intercourse with a new partner.5, 12 Women were followed-up with gynecological examinations every four months. At each visit, self-collected vaginal swabs and clinician-collected cervical and vulvovaginal swabs were collected. Men were seen only for one visit. They underwent a clinician-administered interview about their medical and sexual history and a genital examination including specimen collection from the penis, urethra, and scrotal area, described in detail elsewhere.13 All samples were tested for HPV DNA by polymerase chain reaction (PCR)-based methods. Specimens testing positive by a generic probe were typed using a reverse line-blot assay (Roche Molecular Systems) for 37 distinct HPV types.14 PCR results of vaginal, cervical, and vulvovaginal swabs for women and penile, urethral, and scrotal swabs for men were combined to determine genital HPV status in each participant. Institutional Review Board of the University of Washington approved the study; informed consent was obtained from all participants. Male partners were enrolled for 33 women. Information on 19 couples was excluded due to the following reasons: one woman did not report any sexual activity in the diary; three men were not the first sex partner of their female partner; and 15 couples were not found to be infected with HPV. Of the remaining 14 couples, both partners were found to be infected with HPV in five couples and the male partner only was found to be infected in three couples. Descriptive results for these eight couples and for the other six couples in whom, unexpectedly, the female partner was found to be infected with HPV, while the male partner was not, are provided in Tables 1 and ​and22. Table 1 Characteristics of eight couples in whom at least one type of HPV was detected in the single visit of the first male partner Table 2 Characteristics of six couples in whom at least one type of HPV was detected in the female partner but not in the male partner Investigators who embark upon designing a methodologically sound study to find empirical estimates of male-to-female sexual transmissibility of HPV may face the following difficulties: