Prevalence and incidence of anal human papillomavirus (HPV) are high among young gay men, according to US research published in the Journal of Infectious Diseases. Overall prevalence of anal HPV infection was 70%, and HPV 16 and/or HPV 18 – the HPV types most associated with anal cancer – were detected in 37% of study participants.
The investigators believe their research shows the importance of vaccinating young gay men before they become sexually active. However, none of the men were infected with all four HPV types covered by the quadrivalent vaccine Gardasil, therefore showing that immunisation would still be worthwhile for young gay men who are sexually experienced.
“Our findings highlight the need to immunize YMSM [young men who have sex with men] prior to their sexual debut, something that will likely require universal male immunization,” write the authors. “At the same time, the fact that most YMSM appeared to remain susceptible to at least some HPV types included in the vaccine, catch-up immunization programs do offer YMSM some benefit.”
Rates of anal cancer are higher among gay men than other groups. The cancer is associated with persistent infection with high-risk HPV types. Gardasil provides a high degree of protection against the two most common cancer-associated HPV types (16 and 18). In the US, immunisation with this product is now recommended for all males aged between eleven and 21 years and for gay and other men who have sex with men up to the age of 26 years.
Despite these recommendations, little is currently known about prevalence and incidence of anal HPV infection among young gay men. Investigators in Seattle therefore undertook a prospective study lasting one year involving 94 gay men aged between 16 and 30 years. These participants had anal swabs at baseline, and again after six and twelve months, to check for HPV infection and HPV type. The authors also looked at the factors associated with HPV infection and knowledge of HPV and HPV vaccination. They were hopeful that their findings would inform vaccination strategies.
Most of the men were white (60%) and their median age was 21 years. Nearly all participants reported a history of at least one episode of insertive anal sex (88%) and receptive anal sex (92%). The median age of first anal sex with another man was 18 years. The median number of lifetime, anal-sex, insertive partners was two and the median number of receptive anal sex partners was three.
Overall, 70% of men had anal HPV infection detected at some point during the study. HPV 16 was the type with the highest prevalence (28%).
Among the men who did not have the infection at baseline, the incidence of new anal HPV infection was 39 per 1000 person-months.
HPV 16 and/or 18 infections were detected in 37% of men over the course of the study, with an incidence of 15 per 1000 person-months.
Approximately a fifth of participants (19%) had persistent HPV 16 or 18 infection, with the same strain detected in consecutive swabs.
Half of all participants had at least one of the HPV strains covered by Gardasil detected at some point during the study. However, no participant tested positive for all four types and only 3% had evidence of acquiring both HPV 16 and 18 at the same time during follow-up.
A total of 48 men with any prevalent HPV infection provided two or more swabs. Most of these men (81%) cleared one or more HPV type during follow-up. Half the 18 men with HPV 16 cleared the infection, as did 67% of those with HPV 18.
The prevalence of HPV infection, including the high-risk types, increased with higher numbers of male anal sex partners. Among the men reporting one lifetime anal-sex partner at baseline, 35% had any anal HPV infection and 6% were infected with HPV 16 and/or 18. Among men with two or more partners, there was a 35% prevalence of anal HPV 16 and/or 18 infection.
For each additional partner in the previous three months, the risk of prevalence infection increased by a quarter (OR = 1.24; 95% CI, 1.00-1.57) and the odds of incident infection by a third (OR = 1.32; 95% CI, 1.03-1.70).
There was moderately good knowledge of HPV among the participants, with 76% of men reporting that they had heard of the infection. However, only 34% knew that it was the cause of anal cancer and 6% correctly identified the virus as a cause of oral and throat cancers.
Approximately three-quarters of participants had heard of Gardasil. The investigators explained the vaccine’s treatment course, side-effects and efficacy to the participants, after which 93% of men said they would be extremely or somewhat interested in the vaccine if it were available free of charge.
“We observed a high prevalence and incidence of anal HPV infection,” comment the authors, “HPV-16 and/or -18, the two strains that cause the majority of anal cancers, was detected in over one-third of study participants at least once during the year of follow-up, and nearly 20% of all YMSM in our study had evidence of persistent infection with one of these two strains.”
The investigators believe their findings have implications for HPV vaccination strategies: “Given the very high prevalence of HPV infection among YMSM, many (if not most) have been exposed to infection from one of their first few partners, a finding that highlights the desirability of immunizing YMSM before they become sexually active.” Nevertheless, they also believe that men who are sexually active would also benefit from vaccination.
Glick SN et al. High rates of incident and prevalent anal human papillomavirus infection among young men who have sex with men. J Infect Dis, online edition, 2013.