Anal HPV more prevalent than cervical HPV in HIV-positive women

Research in human papilloma virus (HPV) in women has mostly focused on cervical HPV; not much is known about anal HPV infection in women. A team of American researchers therefore investigated the prevalence (frequency of occurrence) and diversity (number of different viral strains) of HPV in HIV-positive women, finding that the virus is actually more prevalent and more diverse anally than cervically. The research was presented to the recent meeting of the Infectious Diseases Society of America in Toronto.

HPV is the name for a family of sexually transmitted viruses which includes dozens of different subtypes. Some of these subtypes cause genital and anal warts; others can lead to cervical cancer in women, or anal cancer in people of either sex. People with damaged immune systems are at increased risk of HPV-related cancers.

The SUN Study (Study to Understand the Natural History of HIV/AIDS in the Era of Effective Therapy) is a five-year, prospective observational study that aims to enroll 1000 HIV-positive participants through seven U.S. centres. As part of the SUN study, 122 women provided information about sexual risk factors, and had cervical and anal swabs analysed for human papilloma virus. The women ranged between 21 and 64 years of age (average 40), were racially diverse, and had median CD4 cell counts of 419 cells/mm³ and viral load of 1.7 log₁₀.

In all, 112 (92%) of the women were found to have HPV. All strains of HPV were more commonly found by anal than by cervical swab (92% vs. 86%; high-risk types for cancer 84% vs. 64%; low-risk types 74% vs. 59%). A larger number of different HPV subtypes were also found in the anus, as compared to the cervix: this was true at all CD4 count levels, and for high-risk and low-risk subtypes for cancer. The actual subtypes themselves varied: of the types considered high-risk for cancer, types 16, 35, 53, 58 and 59 were most prevalent in the cervix; types 16, 18, 31, 45, 53 and 58 were most prevalent in the anus. (Viral subtypes 16 and 18 are considered the most ‘oncogenic’, or likely to cause cancer: currently available ‘quadrivalent’ HPV vaccines are active against viral subtypes 6, 11, 16 and 18.)

Since the group did not include many women with very low CD4 cell counts, the researchers could not really gauge CD4 count as a risk factor. They did, however, find that having had anal sex did not appear to be a risk factor for anal HPV. They concluded that “there is a need to further investigate the clinical significance of anal HPV infection in women.” Also, since currently available HPV vaccines are based on a few specific high-risk subtypes, they state that “HPV vaccine efficacy needs to be evaluated in HIV-positive women.”