Sexual behaviour and smoking as determinants of cervical HPV infection and of CIN3 among those infected: a case-control study nested within the Manchester cohort.

Abstract

To distinguish risk factors for acquisition of cervical human papillomavirus (HPV) infection from the determinants of neoplasia among infected individuals we have conducted a three-arm case-control study nested within a large population-based cohort of women (the Manchester cohort) screened for HPV at entry using L1 consensus primer PCR. The study includes 181 HPV-positive controls who did not develop high-grade cervical intraepithelial neoplasia (CIN3) during follow-up, 203 HPV-negative controls, and 199 HPV-positive cases with histologically confirmed CIN3. Detailed information on sexual, reproductive and gynaecological history, oral contraceptive use and smoking was obtained at face-to-face interview. There was a striking division between risk factors for infection and those predictive of disease. Comparing the HPV-positive against the HPV-negative controls, the only risk factors for infection were number of sexual partners (OR for six or more = 3.89; 95% Cl = 1.99-7.62), a relatively recent new sexual relationship (OR for a new partner within the previous 2 years = 4.17; 95% Cl = 2.13-8.33), and a history of previous miscarriage (OR = 2.59; 95% Cl = 1.28-5.21). The determinants of CIN3 among infected women were, in contrast, early age at first intercourse (OR for 16 years old or less = 3.23; 95% Cl = 1.33-7.69), a long time since starting a new sexual relationship (OR for 6 years or more = 4.94; 95% Cl = 2.51-9.71), and cigarette smoking, with strong evidence for a dose- response (OR for current smoking habit 20+ per day = 2.57; 95% Cl = 1.49-4.45). Oral contraceptive use was not significantly associated with either HPV infection or CIN3.