Sex- and type-specific genital human papillomavirus transmission rates between heterosexual partners: a Bayesian reanalysis of the HITCH cohort.

BACKGROUND It is unclear whether sexual transmission rates of human papillomaviruses (HPV) differ between sexes and HPV types. We estimate updated transmission rates from the final HITCH cohort study, and propose an estimation method that accounts for interval-censored data and infection clearance. METHODS We enrolled young women 18-24 years old and their male sex partners ≥18 years old in Montreal, Canada between 2005-2011. We followed women over 24 months and men over 4 months. We tested genital samples with Linear Array for HPV DNA detection and genotyping. We calculated infection transmission rates between partners using a multistate Markov model via a Bayesian approach. We report the posterior median and 2.5%-97.5% percentile intervals (95%PI). RESULTS We observed 166 type-specific incident HPV transmission events in 447 women and 402 men. The estimated median transmission rate from an HPV-positive to a negative partner was 4.2 (95%PI 3.1-5.3) per 100 person-months. The transmission rate from men to women was 3.5 (95%PI 2.5-4.7) and from women to men was 5.6 (95%PI 3.8-7.0) per 100 person-months, corresponding to a rate ratio of 1.6 (95%PI 1.0-2.5). Partners reporting always using condoms had a 0.22 (95%PI 0.05-0.61) times lower HPV transmission rate than those reporting never using condoms. HPV16/18 did not have particularly high transmission rates relative to other HPV types. CONCLUSION Our updated analysis supports previous research suggesting higher women-to-men than men-to-women HPV transmission rates and a protective effect of condoms in heterosexual partnerships. Our results also suggest that crude incidence rates underestimate HPV transmission rates due to interval-censoring.