Comparison of two methods of screening for genital chlamydial infection in women attending in general practice: cross sectional survey

Abstract Objectives: To estimate the prevalence of Chlamydia trachomatis in asymptomatic women attending general practice; to assess the potential of the ligase chain reaction as a screening tool; and to evaluate selective screening criteria. Design: Cross sectional survey. Setting: Four general practices in northeast London. Subjects: 890 women aged 18-35 years attending general practice for a cervical smear or a “young well woman” check between October 1994 and January 1996. The women were tested for C trachomatis with confirmed enzyme immunoassay (endocervical specimens) and ligase chain reaction assay on urine specimens. Main outcome measures: Prevalence of C trachomatis infection in women aged 18-35 on the basis of each test; sensitivity and specificity of both tests in this population. Results: Prevalence of confirmed infection was 2.6% (95% confidence interval 1.6% to 3.6%) in all women. Prevalence on the basis of enzyme immunoassay was 1.6% (0.8% to 2.7%), with a sensitivity of 60% and a specificity of 100%. Prevalence on the basis of ligase chain reaction was 2.5% (1.5% to 3.9%), with 90% sensitivity and 99.8% specificity. Screening all women aged ≤25 and all women who had had two or more partners in the past year would have detected 87% (20/23) of infections. Conclusion: Ligase chain reaction on urine samples performs at least as well as enzyme immunoassay on cervical specimens in this low prevalence population. It offers potential as a non-invasive screening tool. A simple selective screening strategy might be appropriate and would be able to detect most cases of infection. However, a rigorous economic evaluation of possible screening strategies is needed first. Key messages Chlamydia trachomatis causes a common sexually transmitted infection, which is often asymptomatic but may lead to pelvic inflammatory disease, ectopic pregnancy, and tubal infertility in 10%-25% of infected women Over 1 in 20 women aged 18-25 years attending general practice may have undiagnosed infection New screening tests that do not require a cervical sample should improve the prospects for community based screening for chlamydia Rigorous evaluation of the cost effectiveness of such screening is now a priority