High rate of new infections with HPV types associated with a high risk of anal cancer among gay men living with HIV

Incidence of anal infection with cancer-associated strains of human papillomavirus (HPV) is high among gay men living with HIV, US investigators report in the online edition of AIDS. Researchers followed a cohort of 369 men for at least two years. There was a 13% annual incidence of anal infection with high-risk HPV types.

The study also confirmed what has been long suspected – that receptive anal sex activities are associated with anal HPV infection. Interestingly, receptive oral-anal contact (rimming) was among the risk factors. The authors believe this to be “an important finding suggesting another potential route of exposure to anal HPV infection. Oral-anal contact also could explain anal HPV infection among men (and women) who deny receptive anal intercourse.”

Anal HPV infection is almost universal among HIV-positive gay and other men who have sex with men (MSM). Infection with certain high-risk HPV types is associated with an increased risk of anal cancer, rates of which are higher among HIV-positive MSM than any other group.

Much of the information about anal HPV infection in MSM living with HIV comes from cross-sectional research. However, such studies have limited ability to examine risk factors, given that cases of HPV will be a mixture of prevalent and new infections.

Investigators in San Francisco therefore designed a prospective study to assess the incidence of and risk factors for anal HPV infection among MSM living with HIV in the era of effective antiretroviral therapy. Recruitment occurred between 1998 and 2000.

Participants in the study had swabs to detect anal HPV infection at six-monthly intervals over a minimum of two years. At each follow-up, they also answered questions about their recent sexual risk behaviour.

The participants had a mean age of 45 years. Over three-quarters (75%) reported a history of anal or genital warts and 92% had prevalent anal HPV present at baseline. Low- or high-grade pre-cancerous anal cell changes were detected in 78% of individuals. Most participants (86%) were taking HIV therapy. Overall, 62% had a suppressed viral load and 37% a CD4 count above 500 cells/mm³.

During follow-up, the annual incidence of anal infection with any HPV type was 21.3 per 100 person-years and was 13.3 per 100 person-years for cancer-associated HPV types. The most common incident infections by type were HPV 18 (3.7 per 100 person-years) and HPV 16 (3.5 per 100 person-years). The authors emphasise these are the two HPV types most associated with anal cancer.

Of the 122 men with any incident anal HPV infection, 80% had an incident infection with one HPV type, 16% with two types, 3% with three types and 1% with four or more types.

Several receptive anal sex behaviours were associated with a significantly increased risk of incident anal HPV infection. These included a higher number of recent partners with whom the participant was receptive. Men with eight or more partners had an almost three-fold increase in their risk of new infection compared to men with one or fewer partners (OR = 2.8; 95% CI, 1.6-5.1, p = 0.002). Frequency of receptive anal intercourse was also another risk factor. Men engaging in this activity at least once a week were significantly more likely to have an incident anal HPV infection than men reporting less frequent receptive anal sex (OR = 2.6; 95% CI, 1.6-4.6, p = 0.004). Each new partner with whom the participant engaged in receptive oral-anal contact also increased the risk of acquiring a new HPV infection (OR = 1.1; 95% CI, 1.03-1.1).

“Our study represents one of the few natural history studies of a cohort of HIV-positive MSM, followed prospectively for anal HPV infection, together with a detailed evaluation of risk factors for infection during the post-ART era,” write the authors. “Almost all indicators of receptive anal intercourse were significantly associated with incident anal HPV infection.”

They conclude, “HIV-positive MSM should be counseled about anal cancer and risk factors for HPV infection. They should also be counseled about primary prevention measures such as condom use and the HPV vaccine.”