DNA methods should be used to detect Chlamydia trachomatis

Editor—We agree with the comments¹ on Boag and Kelly’s editorial² about the recommendations made by the chief medical officer’s expert advisory group on Chlamydia trachomatis. We wish to raise another issue.

The laboratories associated with the genitourinary medicine clinics in the two pilot projects evaluating the proposed screening will use molecular procedures (ligase chain reaction or polymerase chain reaction) and not the less sensitive tests (enzyme immunoassays) used by most laboratories testing for C trachomatis in England and Wales. Support exists for this proposal.³ However, the use of the most sensitive tests should extend beyond this. About 30% of women, symptomatic or asymptomatic, with C trachomatis infection attending genitourinary clinics have small numbers of organisms in cervical specimens.⁴ As most clinics rely on enzyme immunassays the infection will not be diagnosed in most of these women. We calculate, on the basis of about 500 000 women attending genitourinary medicine clinics each year, a prevalence of C trachomatis of about 10%, and about 30% of cases being missed, that in the past 10 years 150 000 women seen in genitourinary medicine clinics will have had a C trachomatis infection overlooked. There could not be a greater indictment of the service.

Some of these women may have received treatment, but most will have remained untreated and falsely reassured. Misdiagnosis is an important reason for C trachomatis persisting in the community and the frequency of pelvic inflammatory disease, ectopic pregnancies, and infertility.

The usual justification for not using the sensitive detection tests is financial restriction. However, ultimately the introduction of DNA amplification tests will be cost effective.⁵ The use of DNA amplification tests by laboratories servicing all clinics, not just those involved in the pilot projects, is long overdue. Pressure should be put on hospital trusts to make sure that the best tests are available. The medicolegal costs of infertility resulting from the failure to identify C trachomatis because inferior tests were used will be high. The current situation would not be tolerated in HIV testing. C trachomatis does not kill, but it causes an immense amount of human suffering.