Sex differences in the incidence and clearance of anal human papillomavirus infection among heterosexual men and women in Liuzhou, China: an observational cohort study: Natural history of anal HPV infection by sex

: Anal cancer is primarily caused by human papillomavirus (HPV) infection in both men and women. However, little is known about the sex differences in the natural history of anal HPV infection in a heterosexual population. From May 2014 to March 2016, perianal/anal canal (PA) swab samples were collected semiannually from 2,302 heterosexual men and 2,371 heterosexual women aged 18-55 years old in Liuzhou, China. The specimens were genotyped for HPV DNA by polymerase chain reaction. The incidence rate ratio (IRR) and clearance rate ratio (CRR) were used to analyze the sex differences of incidence and clearance by Poisson regression, respectively. The incidences of PA oncogenic HPV in men and women were 3.4 per 1,000 person-months and 8.6 per 1,000 person-months, respectively, with an IRR of 0.39 (95% confidence interval (CI), 0.29-0.54 for men versus women) (p < 0.0001). The CRR of PA oncogenic HPV infection for men versus women was 1.54 (95% CI, 1.17-2.03) (p = 0.0022). At 12 months, 44% (20/45) of HPV 16/18 infections among women remained positive, whereas no (0/7) infections persisted among men (p = 0.0350). Both the higher incidence and slower clearance of anal carcinogenic HPV infection among women may lead to a higher burden of anal cancer among women than among men in a heterosexual population.