A new study by Dr. Yurii B. Shvetsov of the Honolulu-based Cancer Research Center of Hawaii and colleagues finds that the STD linked primarily to cervical cancer may also infect the anus, though the infection appears to resolve itself quickly. "This fact may help explain why anal cancer among women is so much rarer than cervical cancer," said Shvetsov.

The researchers assessed factors associated with anal human papillomavirus infection and its clearance by performing a longitudinal study of 431 sexually active women. During an average follow-up of 1.2 years, 50 percent of the women incurred a total of 414 anal HPV infections. Of these infections, 58 percent cleared during follow-up. The average duration of infection from high-risk HPV types was 150 days, though this varied from type to type. The median clearance times for HPV-16 and HPV-18 - the predominant types associated with anal cancer - were 132 days and 212 days, respectively.

"Nonviral factors that delayed clearance of anal HPV included douching, long-term tobacco smoking, and anal sex," the authors wrote.

While testing for cervical HPV can help detect possible cervical cancer, the fact that anal HPV infections are comparatively short-lived raises "the possibility that anal HPV testing might be a less-effective screening tool, as compared to cervical HPV testing," Shvetsov explained.

"Whether or not anal HPV testing should become a generally accepted cancer screening tool is an important question that should be addressed in future studies," the researchers concluded.

The study, "Duration and Clearance of Anal Human Papillomavirus (HPV) Infection Among Women: The Hawaii HPV Cohort Study," was published in Clinical Infectious Diseases (2009;48:536-546).