• Chlamydia Infection
• Sexual Behaviour
• Genitourinary Medicine

Realising the individual and potential population benefits of any chlamydia screening programme depends on good case management. At the very least, this should include the provision of effective and timely antibiotic treatment, finding and treating infected sexual partner(s), and the provision of condoms and safer sex advice.1–3 The papers in this issue and several previously published studies lead us to question whether retesting of people who test positive should also be a routine part of clinical practice. Several countries already recommend retesting 3–12 months after a chlamydia diagnosis.4–7 In England, the National Chlamydia Screening Programme (NCSP) recommends that sexually active young adults be tested annually and on change of sexual partner, but there is no recommendation to routinely retest positives more frequently.3 Should there be?

The clinical arguments for retesting are strong. First, we know from prospective8–11 and passive12 ,13 follow-up studies that individuals who test positive for chlamydia are at considerably higher risk of subsequent chlamydia infection than those who test negative. Retesting could therefore lead to considerably greater numbers of infections being diagnosed and treated. In a prospective cohort study of 16–24-year-old women tested in general practice, family planning or genitourinary medicine clinics in England in 2002–2003, participants were tested at baseline and 6-monthly intervals, with an additional test at 3 months after a positive test. In those accepting repeat testing, rates of re-infection were 2–6 times higher than rates of incident infection. Among women tested in family planning settings, for example, there were six incident infections per 100 person years following a negative test, compared with 22 per 100 person years following a positive test.8 Similar findings have been reported from studies in Australia,9 the USA10 and the Netherlands.11 Second, because retesting could lead to earlier diagnosis and treatment of repeat infections, risk of onward transmission and development of long-term sequelae may be reduced. Mathematical modelling has demonstrated that re-infections are likely to be important for sustaining chlamydia epidemics14 and observational studies and animal models indicate that repeat exposure to chlamydial infection may considerably increase the risk of severe reproductive tract morbidity.15 ,16

If a recommendation for routine retesting of positives were introduced, what would be the optimum interval for retesting post-treatment? A testing interval of at least 6 weeks is needed to minimise false positives.2 Re-infection may result following re-exposure to an existing (untreated) partner or exposure to a new partner and is therefore influenced by the effectiveness of partner notification immediately following infection as well as partner change in the longer term. Mathematical modelling in the USA suggests repeat infections peak 2–5 months after initial infection,17 but the impact of repeat testing at different intervals on chlamydia prevalence or the incidence of sequelae is unknown. Patient preference and logistical considerations for clinical services are also likely to vary. Thus, the optimum testing interval would need to balance the biological evidence against the practicalities of implementation.

The effectiveness and cost effectiveness of retesting following a positive test will vary according to method of implementation. The least intensive (and least expensive) approach would be to give clinical advice at diagnosis without active follow-up. However, experience in the USA, Australia and New Zealand suggests that recommendations to retest following a positive diagnosis do not necessarily lead to high rates of retesting.18–21 In a study in GP settings in Australia, Bowring et al revealed substantial missed opportunities for retesting, with almost a third of eligible young adults remaining untested at repeat visits within 4 months. The authors propose that automatic computer prompts for clinicians may improve opportunistic retesting rates in these settings.20 More proactive approaches could involve active recall of those who test positive using telephone, email or text message reminders, issuing home self-sampling kits or providing advice to order a self-sampling kit through the internet. These proactive options require more local infrastructure and resources, but, unsurprisingly, tend to be more effective.22–24 The cost implications for any change in service delivery will have to be considered.

Routine retesting of those who test positive for chlamydia could yield considerable public health benefit. Different approaches should be evaluated in the context of the existing NCSP recommendation for testing on change of sexual partner, and in terms of feasibility, effectiveness, cost per test and additional infection identified, and acceptability among service users and service providers. Examining the potential for unintended harmful consequences will also be essential. Last, but by no means least, it is important to remember that re-infection reflects repeat exposure and is not inevitable; it is preventable. Effective partner notification and management, as well as risk-reduction counselling promoting condom use and behavioural change in those diagnosed with chlamydial infection, should not be forgotten in the discussion around retesting.25

The NCSP in England will continue to promote opportunistic chlamydia screening of sexually active young adults and to encourage safer sexual behaviour. The time is now right to determine whether routine repeat testing of positives should become part of the standard toolkit for managing those infected and, if so, how best to implement it.