There is a strong rationale for systematic Chlamydia screening, and it is widely recommended and practised. Yet there are harms associated with the screening process (Low(STIs)), and, of course, serious concerns about its cost-effectiveness (De Wit & Kretzschmar (STIs)).  This lends urgency to the question of whether Chlamydia screening works – addressed in a recently published systematic review for the Cochrane Database:  ‘Screening for genital chlamydia infection’.

It all depends, the authors claim, on what we want screening to do: whether it’s a general reduction of prevalence in the population that we’re aiming at, or the prevention of serious sequelae such as PID (Pelvic Inflammatory Disease) in individuals.  The strict Cochrane exclusion criteria (especially that of ‘reporting a pre-specified primary outcome’) reduce the pool of evaluated studies to just two addressing the impact of screening on Chlamydia prevalence – only one of which (not, as it happens, an RCT) addresses impact on prevalence in the general population (Schmid & Kretzschmar (STIs)).  Regarding the impact of screening on reduction of PID incidence, the field narrows to just four RCTs (Andersen & Olesen (STIs);  Ostergaard & Olesen; Oakeshott & Hay; Scholes & Stamm).

Respecting the impact on prevalence, Schmid & Kretzschmar (STIs) observe very little effect (RR 0.96), but the quality of evidence is rated, on Cochrane criteria, as ‘low’.  As for PID prevention, an effect was observed (overall RR 0.68), but unfortunately was considerably less pronounced in the two studies with low risk of selection bias (Andersen & Olesen (STIs) and Oakeshott & Hay) (RR 0.80) than with the other two studies ((RR 0.42).  This evidence was consequently downgraded from ‘high’ to ‘moderate’.

So there continues to be no evidence at present for a positive impact of screening on general prevalence, though further research could possibly modify this assessment.  As regards the incidence of PID, some limited degree of positive impact may have been demonstrated – though whether systematic screening interventions will turn out to be cost-effective is another question (De Wit & Kretzschmar (STIs)).  The reviewers point out there is another important trial that is still on-going (hence not eligible for inclusion): Hocking (STIs).  The latter – a study being undertaken in Australian GP practices – involves ‘opportunistic’ testing (as defined by Low (Low(STIs)) rather than screening proper (i.e. ‘systematic’ screening).  However, given that this is the form of intervention being undertaken in many places including the UK, its final results will no doubt be of great interest.  On the basis of the study’s findings to date, the verdict seems unlikely to be favourable (Yeung & Temple-Smith (STIs)).