Controlling genital chlamydial infection

Advances in diagnosis and treatment may make screening worthwhile

Screening for asymptomatic Chlamydia trachomatis was first proposed in the early 1980s1 and guidelines for selective screening in the United States were published by the Centers for Disease Control in 1993.2 The condition fulfils many of the criteria for screening.3 Most infections are initially asymptomatic but may subsequently cause considerable long term morbidity.4 5 Treatment is simple and effective. So, is genital chlamydial infection worthy of a national selective screening programme in Britain?

C trachomatis is the most common curable sexually transmitted pathogen in Britain. Despite previous calls for more attention to be paid to the problem,6 no national screening guidelines are in place, although the Department of Health has recently formed an expert advisory group to address questions of control. The epidemiology of genital chlamydial infection has been incompletely studied. Screening, diagnosis, and treatment remain inconsistent. National surveillance of chlamydial infection is limited to returns from genitourinary medicine clinics and voluntary laboratory reporting.

Over 39 000 cases of genital chlamydial infection were treated in genitourinary medicine clinics in England and Wales in 1995, more than three times the number of cases of gonorrhoea reported.7 It is well recognised that chlamydial infections are often asymptomatic in both men and women and may therefore go untreated.8 9 The age specific prevalence in the general population has never been adequately measured. Surveys in women attending general practices in Britain, using variable selection criteria, show prevalences ranging from 2–12% with highest prevalence in those less than 25 years of age and in women requesting termination of pregnancy.10

In this week's BMJ, Ross et al (p 1192) show that most chlamydial infections diagnosed by general practitioners in Lothian are not referred to genitourinary medicine clinics.11 Though this does not tell us what proportion of all chlamydial infections are treated in general practice, it does suggest that general practitioners have an important role in detecting infection. It also suggests, along with a second paper (p 1193),12 that current management by general practitioners is suboptimal, either because of inappropriate antibiotic treatment or because sexual partners are not traced and treated.

Genital chlamydial infection in women has serious sequelae. Untreated C trachomatis infection can persist for long periods, and up to 30% of inadequately treated women may go on to develop pelvic inflammatory disease.4 Up to half of all cases of pelvic inflammatory disease in developed countries can be attributed to chlamydia.5 Among those with symptomatic pelvic inflammatory disease, one fifth may become infertile and one tenth suffer ectopic pregnancy. The personal and economic costs of untreated genital chlamydial infection are considerable.

The first randomised controlled trial of selective chlamydial screening in women aged 18–34 enrolled in a health maintenance organisation in the United States was published last year.13 The incidence of pelvic inflammatory disease at one year was 56% lower in the screened than in the unscreened arm. This strengthens evidence from observational studies in the United States and Scandinavia that programmes of chlamydial screening, primarily in women,14 can reduce the prevalence of infection over time.

The screening programmes described above all used conventional methods of chlamydial diagnosis, all of which are limited by low sensitivity.15 Diagnostic testing for C trachomatis has recently been substantially improved by the introduction of DNA amplification techniques, particularly the ligase chain reaction assay.16 No single test can identify all cases of C trachomatis infection.17 Nevertheless, a single ligase chain reaction assay on urine may perform better (in terms of both specificity and sensitivity) than previously available tests.16 Ligase chain reaction tests cost about twice as much as enzyme immunoassays but detect considerably more cases.16 17

The most attractive aspect of DNA amplification methods is their good performance on urine. This makes non-invasive screening possible, which is likely to be more acceptable and minimises use of clinical time. On p 1186, Oostergaard et al report that DNA amplification methods on endocervical and urethral samples collected by general practitioners, and on urine and vaginal samples collected by women at home, were equally effective in detecting cases.18

Antibiotic treatment of C trachomatis is straightforward, and single dose treatment is a recent advance. Single oral dose treatment with azithromycin (1 g) has been shown to be as effective as treatment with oral doxycycline (100 mg twice daily for seven days). Though azithromycin costs twice as much as doxycycline, economic evaluation suggests that it may be more cost effective in practice because compliance is greater.19 Treatment of partners is a key component of control. Yet, as Mason et al confirm,12 contact tracing for chlamydia is poor in many settings and may fail to attract the attention paid to gonorrhoea, even in genitourinary medicine clinics.20

What action is appropriate on selective screening? American guidelines currently suggest annual screening of women with mucopurulent cervicitis, all sexually active women under that 20 years of age, and women over the age of 20 selected on the basis of inconsistent use of barrier contraception and partner change.2 In Britain, studies of effectiveness of different selective screening strategies are needed. Cost effectiveness of screening needs to be measured in terms of averting longer term sequelae. Such economic evaluation must take into account the prevalence of infection, the cost and performance of tests, the location and frequency of screening, and protocols for treatment and contact tracing.

Genital chlamydia infection may not often be life threatening but it can be life ruining and has major costs for both the health service and the individual. Recent advances in diagnosis and treatment of C trachomatis have appreciably improved the prospects of controlling this neglected condition.

We thank Drs Judith Stephenson and Geoffrey Ridgway for their helpful comments.