There are two types of screening - proactive and opportunistic. Proactive screening uses population registers to invite people to be screened regularly, while opportunistic screening targets people attending health services for unrelated reasons.
In England, chlamydia screening is mainly opportunistic, but in some areas general practices registers are being used to send proactive invitations to potentially eligible people to remind them to be re-screened.
Most studies have suggested that chlamydia screening is cost-effective, but there are now questions surrounding the validity of these results. So researchers set out to compare the cost effectiveness of proactive screening with a policy of no organised screening.
Using a mathematical model, screening was offered proactively to a hypothetical population of 50,000 men and women aged 16-24 years. A dynamic model was used to give the closest possible approximation to the real sexual behaviour of this population.
Previous studies have used static models that are inappropriate for evaluating an infectious disease.
The cost-effectiveness of screening was based on major outcomes averted, defined as pelvic inflammatory disease, ectopic pregnancy, infertility, or neonatal complications.
For screening men and women, the incremental cost effectiveness ratio per major outcome averted after eight years was approximately Ģ28,900 compared with no organised screening. It was less costly to screen women only but also less effective, and the incremental cost effectiveness ratio per major outcome averted was approximately Ģ22,300.
Pelvic inflammatory disease was the most frequently avoided outcome.
When the incidence of major complications and uptake of screening were increased (but to values unlikely to be seen in real life), the cost effectiveness ratio fell to Ģ6,200 per major outcome averted for screening women only.
The authors conclude: "Our evaluation of proactive population chlamydia screening, using a dynamic model incorporating realistic estimates of partner notification, the uptake of screening, and the incidence of severe complications, has shown it to be an expensive intervention that probably does not represent good value for money."
The recent economic evaluation of the National Chlamydia Screening Programme in England shows that opportunistic screening, which is currently being rolled out across England, is also unlikely to be cost-effective. This paper was first published in May 2007, ahead of print, in the journal Sexually Transmitted Infections and will appear in print on 30 July.