Risk factors for squamous intraepithelial lesions (SIL) of the cervix among women residing at the US-Mexico border.

It is now well established that cervical cancer is caused by oncogenic human papillomavirus (HPV) infections that commonly infect women worldwide. What remains to be understood are the factors that contribute to cervical cancer in the presence of HPV infection. We conducted a case-control analysis of women recruited at the US-Mexico border to simultaneously evaluate factors associated with 3 cytologic outcomes: atypical squamous cells of undetermined significance or atypical glandular cells of undetermined significance (ASCUS/AGUS), low grade squamous intraepithelial lesions (LSIL) and high grade squamous intraepithelial lesions (HSIL). A cross-sectional binational study of 2059 women ages 15-79 years was conducted between 1997 and 1998. A significant difference in the distribution of cytologic categories by country was observed (3.0% vs. 0.7% HSIL among Mexican vs. US women, respectively). The only factors independently associated with all 3 cytologic outcomes were HPV infection and viral load. A linear increase in risk with increasing viral load was observed for each of the 3 outcome variables, with the strength of this association increasing with cytology abnormality. In addition to HPV infection, parity and Mexico as a country of residence appear to be associated with LSIL and HSIL, respectively. Factors associated with cytologic outcomes in analyses limited to women with HPV infection were similar to results obtained in models where HPV infection was included as a covariate. Future work is needed to evaluate the predictive value of HPV viral load utilizing more specific and quantitative measures.