Can a case be made for opportunistic testing for Chlamydia?

Last month saw the publication of a revised Guidance on Chlamydia Control in Europe (2016) by the European Centre for Disease Prevention and Control.  This replaces the earlier Guidance on Chlamydia Control in Europe (2009) – though the 2016 document refers the reader to the 2009 one for more detailed descriptions of the epidemiology of the infection in Europe, and of prevention programmes in the various states.  The 2016 Guidance displays a distinct change in tone from the earlier document, reflecting greater scepticism as to the feasibility of an ‘effective Chlamydia control strategy’ and abandoning the earlier ‘step-by-step’ presentation with its suggestion of ascending levels culminating in register-based screening.  The changes concern primarily opportunistic testing and screening (formerly levels C and D in the ascending sequence).  These interventions are now recommended only ‘if resources are available’.

So what sort of case can be made for Chlamydia prevention interventions that go beyond primary prevention to at-risk individuals, evidence-based case management, and partner notification?

In favour of asymptomatic testing it is sometimes argued that the sequelae of Chlamydia such as Pelvic Inflammatory Disease (PID), ectopic pregnancy and tubal infertility largely occur in patients who have experienced only asymptomatic infection; so interventions restricted to treating symptomatic patients and their partners are likely to have limited impact on the prevention of complications (see Low, and response by Joan M. Chow).  On the other hand, it has proved very difficult, in practice, to come up with opportunistic testing interventions that can be shown to be effective (see Low).  As far as concerns the population level impact of such interventions, it seems unreasonable, on current evidence, to expect that they would ever be able to achieve sufficiently high levels of coverage.  However, If we limit our interest to their impact at the individual level, the effectiveness of opportunistic testing turns out to be very difficult to evaluate, because insufficient is known, amongst other things, about the risk of Chlamydia progressing to complications.  And without knowing more about the effectiveness of interventions, it is difficult to produce a robust evaluation of their cost effectiveness.

Some attempts have been made, however.  De Wit & Kretzschmar/STIs (D&K) model various screening scenarios on the basis of data from a three year annual screening programme in an area of the Netherlands that was genuinely register-based – as opposed to the opportunistic testing undertaken by the so-called ‘screening’ programme in the UK.  Andersen & Valkengoed/STIs (A&V) report on the Danish ‘register’ study which randomly assigned 9000 from the public register either to be invited or not invited for a Chlamydia test, and then followed up both arms for Chlamydia sequelae over a nine-year period.  From neither study are the results particularly encouraging.  D&K estimate cost effectiveness, on the most favourable scenario, at over $50,000 per QALY; while A&V report no benefit from participation in the intervention arm which received invitation to a Chlamydia test.

As for opportunistic testing, Johnson & Cassell/STIs (J&C) compare the various institutional settings involved in UK national programme in respect to the number of tests performed and the rates of positivity – as do den Heijer & Dukers- Muijrers/STIs (d&D) for the South Limburg area of the Netherlands in study on a registered based intervention (see also Woodhall & Saunders/STIs).  J&C remark on the relative importance for women of healthcare-based settings along with youth centres, both as regards number of tests performed and positivity.  This happens to agree with the findings of d&D who report 71% of female positive diagnoses in healthcare settings.  For men, non-healthcare related institutional settings were popular, but had considerably lower rates of positivity than healthcare-related settings.

Overall, these papers seem to indicate the likely effectiveness of opportunistic testing through enhanced testing services in healthcare-related settings –a solution that might be achievable without undue cost through existing health services.

 

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