HPV-cytology Testing Versus Cytology Testing for the Detection of High Grade CIN

To compare the effects of conventional cytology testing with concommitant HPV-cytology testing for the detection of high grade cervical lesions in primary cervical cancer screening in Hong Kong Hypotheses: 1. There is a significant difference in the number of CIN2+ cases detected between the cytology testing group and the cytology-HPV co-testing group at baseline. 2. Significantly more CIN2+ cases will be detected at the second round of screening among participants with normal cytology result in the control arm than those with normal cytology and negative HPV results in the intervention arm.