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Incidence and Duration of Cervical Human Papillomavirus 6, 11, 16, and 18 Infections in Young Women: An Evaluation from Multiple Analytic Perspectives

Departments of ¹ Health Economic Statistics, ² Epidemiology, and ³ Clinical Research-Vaccines and Biologics, Merck Research Laboratories, North Wales, Pennsylvania

Requests for reprints: Ralph P. Insinga, Merck & Co., Inc., UG1C-60, P. O. Box 1000, North Wales, PA 19454-1099. Phone: 267-305-7992; Fax: 267-305-6455. E-mail: ralph_insinga{at}merck.com

Objective: To estimate the incidence and duration of cervical human papillomavirus (HPV)-6, HPV-11, HPV-16, and HPV-18 infections in a population of young American women.

Methods: The study population consisted of U.S. women who at baseline were 16 to 23 years of age, reported zero to five lifetime sexual partners, never having been pregnant, and never having had a prior abnormal Papanicolaou test and were enrolled in the placebo arm of a randomized multicenter clinical trial of a HPV-16 L1 virus-like particle vaccine. Women underwent type-specific endocervical/ectocervical swab HPV DNA testing at 6-month intervals for up to 48 months of follow-up. To contribute person-time in the analyses of type-specific HPV incidence, a woman must have had at least three satisfactory swab specimens available and been negative for the relevant HPV type (HPV-6, HPV-11, HPV-16, or HPV-18) on her first two trial swabs. The duration of incident HPV infections was estimated using Kaplan-Meier survival analysis methods.

Results: Person-years of exposure ranged by type-specific analysis from 2,645 to 3,188, with an incidence rate per 100 person-years of 3.6 for HPV-6, 0.4 for HPV-11, 5.4 for HPV-16, and 2.1 for HPV-18. With censoring at the time of treatment for cervical intraepithelial neoplasia, where done, the mean duration of incident infections was 9.3, 8.4, 18.2, and 16.4 months, respectively, for HPV-6 (n = 103), HPV-11 (n = 13), HPV-16 (n = 142), and HPV-18 (n = 62). When the duration of HPV infections was truncated at the time of cervical intraepithelial neoplasia detection (any grade), where applicable, mean duration figures were 8.4, 8.1, 14.0, and 15.1 months for HPV-6, HPV-11, HPV-16, and HPV-18 infections, respectively.

Conclusions: Previous studies of the mean duration of cervical HPV infection have been based on prevalent infections and/or featured relatively short duration of follow-up. This study tested women for HPV infection over a period of up to 48 months and observed a mean duration of incident HPV-16/HPV-18 infections approximately twice that of HPV-6/HPV-11. (Cancer Epidemiol Biomarkers Prev 2007;16(4):709–15)

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