Circumcised men appear more likely to clear human papillomavirus (HPV) infections, including those with oncogenic (cancer-causing) strains, according to a prospective US cohort study published in the Journal of Infectious Diseases. Men with higher numbers of sexual partners were more likely to be infected with HPV, but also appeared more likely to clear oncogenic infections.
HPV is a sexually transmitted virus that can cause genital and anal warts; prolonged infection with certain (oncogenic) strains can lead to anal, cervical and penile cancer.
The HPV Infection in Men study recruited 18- to 44-year-old men in Tucson, Arizona, with no history of genital warts, penile or anal cancer, and no current sexually transmitted infections (including HIV and hepatitis C). Of 377 men screened between 2003 and 2005, data from at least two study visits was available for 285 (median follow-up, 15.5 months). Most (88%) were circumcised, 26% had previous sexually transmitted infections (STIs), and 41% had not used condoms in the past three months.
No data on the sex of the men's sexual partners was provided, and the study only investigated penile, not anal, HPV infection. Over twelve months, 29.2% of the men acquired a new HPV infection: 19% with oncogenic and 16% with non-oncogenic strains (some men acquired both).
In multivariate analysis (adjusting for all other factors), only the total number of lifetime sexual partners affected the risk of new (incident) HPV infections. Men with more than 16 partners were more likely to become infected with HPV (adjusted hazard ratio [AHR], 2.8; 95% confidence interval [CI], 1.1 – 7.1), oncogenic HPV (AHR, 9.6; 95% CI, 2.4 – 37.8) and non-oncogenic HPV (AHR, 3.6; 95% CI, 1.3 – 9.9) than men with zero to four partners (p new HPV infections, not the cumulative risk of sustained HPV infection overall.)
The estimated median time to clearance of new infections was roughly six months. (However, as study visits were six months apart, shorter times could not be distinguished.) By multivariate analysis, circumcised men were three times more likely to clear HPV infections (AHR, 3.1; 95% CI, 1.2 – 8.2) and six times more likely to clear oncogenic infections (AHR, 6.5; 95% CI, 2.1 – 19.7). Men with over 16 lifetime sex partners were five times more likely (AHR, 4.9; 95% CI, 1.2 – 19.8) to clear oncogenic HPV infection than those with zero to four partners, even though these men were also more susceptible to HPV infection.
Other studies have also found a link between the number of sexual partners and, firstly, the risk of infection and, secondly, the likelihood of clearance. Previous researchers have suggested that previous exposures may lead to a greater antibody response to new HPV infections, increasing the chance of clearance. However, it is unclear why previous exposure might also increase the susceptibility to new infection. The reason that circumcision protects against persistence of infection, rather than protecting against infection itself, is also unclear, although it is also consistent with findings of other studies.
Study limitations included the relatively small sample and the uncertainty as to the exact dates of infection and clearance, due to the six-month study visit interval. Nevertheless, the authors concluded that "the key factor associated with acquisition of HPV infection of all types … was lifetime number of sex partners, whereas the most important determinant of clearance of any [penile] HPV infection and of clearance of oncogenic HPV infection was circumcision."
Lu B et al. Factors associated with acquisition and clearance of human papillomavirus infection in a cohort of US men: a prospective study.J Infect Dis 199:362-71, 2009.