There was considerable variation among HPV types with regard to the duration of infection. Coinfection with multiple types contributed to an increased infection duration.

There is paucity of data on whether or not women can be re-infected with human papillomavirus (HPV) types to which they were exposed earlier in life and on the role of natural immunity. The observation of HPV infection at older ages may be explained by reactivation of a latent infection or new exposure from sexual activity. Our objective was to analyze the association between re-infection and sexual activity. We analyzed data from 2462 women enrolled in the Ludwig-McGill cohort and followed every 4-6 months for up to 10 years. We performed HPV typing and viral load measurements via polymerase chain reaction and determined HPV-16 seroreactivity at enrolment. Incidence of infection and re-infection were estimated for individual types. Adjusted relative risks (RR) for the association between infection/re-infection and new sexual partners were calculated using Cox regression. Rates of initial infection and re-infection post-clearance were statistically comparable. RRs of initial infection or re-infection were consistently associated with new sexual partners (2.4 [95%CI: 2.0-3.1] for first infection, 3.7 [1.1-13.8] for re-infection with the same type, and 2.3 [1.5-3.7] for re-infection with a different type). Re-infection in older women was also associated with new sexual partners (RR=2.8, 95%CI: 1.4-5.3) as were new infections with HPV-16 among women with serological evidence of prior HPV-16 exposure (RR=3.0, 95%CI: 1.6-5.3). Viral loads at initial infection and at re-infection were comparable. HPV infection and re-infection were strongly associated with sexual activity. This study suggests that natural immunity does not play a role in controlling the extent of re-infections.