Risk factors for abnormal anal cytology in young heterosexual women.

Although anal cancers are up to four times more common in women than men, little is known about the natural history of anal human papillomavirus (HPV) infections and HPV-related anal lesions in women. This study reports on the prevalence of and risks for anal cytological abnormalities over a 1-year period in a cohort of young women participating in a study of the natural history of cervical HPV infection. In addition to their regularly scheduled sexual behavior interviews and cervical testing, consenting women received anal HPV DNA and cytological testing. Anal cytology smears were obtained from 410 women whose mean age was 22.5 +/- 2.5 years at the onset of the study. Sixteen women (3.9%) were found to have abnormal anal cytology: 4 women had low-grade squamous intraepithelial lesions (SILs) or condyloma; and 12 women had atypical cells of undetermined significance. Factors found to be significantly associated with abnormal anal cytology were a history of anal sex [odds ratio (OR), 6.90; 95% confidence interval (CI), 1.7-47.2], a history of cervical SILs (OR, 4.13; 95% CI, 1.3-14.9), and a current anal HPV infection (OR, 12.28; 95% CI, 3.9-43.5). The strong association between anal intercourse and the development of HPV-induced SILs supports the role of sexual transmission of HPV in anal SILs. Young women who had engaged in anal intercourse or had a history of cervical SILs were found to be at highest risk.