Over a third of gay men infected with strain of HPV most associated with anal cancer

Anal infection with human papilloma virus (HPV) is at near universal levels in gay men, a study conducted in Australia and published in the online edition of Sexually Transmitted Infections has found. Significant numbers of men were infected with strains of the virus that carry a high risk of cancerous and pre-cancerous cell changes in the anus.

The investigators also found that levels of human papilloma virus infection were particularly high in HIV-positive gay men, who were also more likely to be infected with multiple strains of HPV.

Although rare, rates of anal cancer are higher amongst gay man, particularly those with HIV, than in the general population.

Infection with certain strains of human papilloma virus, particularly HPV-16, have been strongly linked to the development of anal cancer. However, there is little information on the prevalence of strains of anal HPV infection in gay men.

Researchers in Sydney, Australia, therefore conducted a study involving both HIV-positive and HIV-negative gay men who were recruited from the community.

A total of 127 HIV-positive and 204 HIV-negative men were included in the study and all had anal swabs. These were analysed in the laboratory using two testing methods to determine the prevalence of human papilloma virus, to determine the virus’s DNA, and to see which strains of the virus were present.

Anal HPV infection was found in 79% of men overall. The prevalence was significantly higher in HIV-positive men (94%) than HIV-negative men (70%, p < 0.0001).

A majority of men were infected with strains of human papilloma virus considered high risk for the development of pre-cancerous and cancerous cell changes in the anus. The prevalence of such strains was significantly higher in HIV-positive men than HIV-negative men (88% vs 56%, p < 0.0001).

The risk of infection with human papilloma virus was not affected by age. Nor was there any difference in prevalence of infection amongst HIV-positive gay men with CD4 cell counts above or below 350 cells/mm³.

In HIV-positive men, the only factor significantly associated with the detection of anal infection with high-risk strains of HPV was anal bleeding in the previous twelve months (odds ratio [OR] 8.36, 95% confidence interval [CI] 1.05 to 66.0).

However, the investigators’ first set of statistical analysis found that there were multiple risk factors for anal infection with high-risk strains in HIV-negative men. These included a history of anal warts, anal infection with gonorrhoea or chlamydia in the previous twelve months, infection with herpex simplex virus-2, and more than 500 lifetime sexual partners. But subsequent multivariate analysis that controlled for potential confounding factors showed that only a history of anal warts was significant (OR 3, 95% CI 1.30 to 6.81).

The samples from 93 HIV-negative men and 36 HIV-positive men were further analysed using tests to study the DNA of human papilloma virus and its strain or genotype. The prevalence of infection with strains of human papilloma virus with a low risk of cancer was similar between HIV-positive (89%) and HIV-negative (87%) men.

However, significantly more HIV-positive men (94%) than HIV-negative men (73%) had infection with high-risk strains.

Of the high risk strains, HPV-16 was found in 36% of HIV-positive men and 27% of HIV-negative men.

More than one strain of human papilloma virus was found in 86% of men. The mean number of strains present in HIV-positive men was seven, versus a mean of four strains in HIV-negative men.

“In this community-based population of sexually active homosexual men, anal human papilloma infection was near universal,” comment the investigators. They add, “A wide variety of…genotypes was detected, and co-infection with multiple genotypes was common. An alarming one-third of participants tested positive for HPV-16, the primary causal agent of anal cancer.”

The investigators call for larger studies “to asses the natural history of anal human papilloma virus infection in homosexual men. The utility of currently available human papilloma virus vaccines would be informed by further population-based data on the human papilloma virus types isolated from anal cancers in homosexual men.”