Objectives: To evaluate the effectiveness of the Pap smear screening programme in Thailand in the prevention of invasive cervical cancer.
Setting: Four tertiary hospitals, in two provinces of north-east Thailand.
Methods: A hospital-based case-control study of women aged 30-64, who were resident in north-east Thailand. A total of 130 women with a diagnosis of invasive cervical cancer were compared with two groups of controls: a) hospital controls, b) hospital patient companions. Information on risk factors for cervical cancer and history of screening by cytology (Pap smear) were collected using a structured interview.
Results: Eighty percent of control subjects reported having had a Pap test in the past, and some two-thirds within the three years before interview. There was a significant protective effect for multiple (6+) previous screening tests as reported by 20% of controls. When women who had tests less than six months prior to the study were excluded, there was a strong, significant protective effect of the number of tests (for 1-5 tests: OR = 0.45 95% CI = 0.25 to 0.84, and for 6+ tests: OR = 0.29 95% CI = 0.11 to 0.82). Tests carried out 1-2 years and 3+ years before diagnosis were associated with an OR of 0.27 (95% CI = 0.13-0.56) and 0.42 (95% CI = 0.20-0.88), respectively.
Conclusions: The cervical screening programme in north-east Thailand has achieved excellent coverage and is preventing cervical cancer. Women who have been screened multiple times are at substantially lower risk than those only screened a few times suggesting that the quality of the screening could be improved.