Human papillomavirus (HPV) is often associated with cisgender women because it can cause cervical cancer -- sexually active women are told to get regular HPV tests, and when the HPV vaccine first came out, it was specifically marketed to parents of girls. Prevalence of HPV is high among everyone, however, and a new study suggests that cisgender men who have sex with men (MSM) have similar rates of four high-risk types of HPV as cisgender women, while cisgender men who have sex with cisgender women (MSW) have slightly lower rates. The researchers believe that this has to do with the type of skin exposed to infection during sex.
HPV is actually a group of more than 200 related viruses that can infect various parts of the body. There are 40 strains of the virus that are known to be spread through sexual activity. The Centers for Disease Control and Prevention (CDC) estimates that 79 million people in the United States are infected with sexually transmitted HPV and 14 million new infections occur annually. Though most people won't suffer long-term health consequences and may never know they have the virus, others may develop cervical cancer or cancers of the head, neck, throat, penis, or anus.
Certain types of the virus are known to cause health issues. Specifically, types 6 and 11 cause most cases of genital warts, and types 16 and 18 cause 70% of cervical cancer. The newest version of the HPV vaccine, called Gardasil 9, protects against these four types as well as five other high-risk types (31, 33, 45, 52, and 58).
For this prevalence study, researchers used data from the National Health and Nutrition Examination Survey (NHANES), which collects information from a nationally representative pool of noninstitutionalized adults. Participants complete a survey that includes questions about sexual behavior and visit a mobile exam center where they are tested for HPV among other things. This study used data collected between 2003 and 2010. This analysis included only sexually experienced, unvaccinated individuals who completed a full sexual history and had been tested for HPV types 6, 11, 16, and 18. The results are, therefore, based on 169 MSM, 6,074 women, and 5,325 MSW.
Overall, the analysis found that HPV seroprevalence was similar in MSM (42.6%) and women (37.1%). In contrast, MSW had a seroprevalence rate of just 13.2%. Among all groups, there were significant differences in prevalence of HPV based on lifetime number of partners, with those people reporting one to four partners having lower rates than those reporting more than 10. This was the only significant difference by demographic characteristic of MSM. Among MSW, seroprevalence also differed by race/ethnicity. Among women, significant differences were seen based on all demographic characteristics, including income, race/ethnicity, and age. The highest rates for women were among non-Hispanic black women (54.5%), 30 to 39 year olds (42.6%), those below poverty (46.5%), and those reporting more than 10 lifetime sex partners (56.1%).
The researchers believe that the differences they found between MSM, women, and MSW are based on likely sexual behaviors and the type of skin at likely infection points -- specifically, keratinized versus non-keratinized epithelium. Non-keratinized epithelium is the thin skin of mucous membranes. It is the skin that has to be kept moist, such as the skin in our mouth, throat, anus, vagina, and cervix. This skin is more prone to micro-abrasions, especially during sex. Keratinized epithelium is thicker and less likely to tear.
This theory would put women who are likely exposed to HPV in their vaginas, cervixes, or mouths at similar risk to MSM, who engage in receptive oral or anal intercourse. MSW would have less risk, because the skin on the penis is more protective.
The researchers also examined seroprevalence of HPV strains 6 and 11 and HPV strains 16 and 18 separately. They found that prevalence of 6 and 11 was higher in MSM (35.7%) than it was in women (25.1%) or MSW (8.5%). HPV 16 and 18 were similar in MSM (19.1%) and women (21.8%) and lower in MSW (6.2%). The authors suggest that these differences by type could be due to the type of infection but might also be due to differences in seroconversion and possible protection provided by previous HPV infections.
This study has limitations because the sample of MSM was so small. That said, the authors still believe it is an important contribution: "Few studies have been able to estimate seroprevalence separately for MSM, MSW, and females," they write. "Even after accounting for sexual behavior, we found significant differences in HPV seroprevalence that may be explained by biological characteristics at the anatomic site of exposure. If naturally acquired antibodies provide protection, variations in seroprevalence among these groups may indicate differences in susceptibility to future infection."