• cost effectiveness analysis
• Chlamydia trachomatis
• screening
• pelvic inflammatory disease

In the December issue of STI, Honey et al summarise and critically review studies of cost effectiveness analysis (CEA) of Chlamydia trachomatis screening to provide recommendations for future screening studies.¹ The authors conclude that screening is cost effective because future sequelae of untreated infection are prevented. They point out that evidence is limited for the probabilities of sequelae of untreated infection used in CEA modelling. A second issue revolves around diagnostic testing. Chlamydia screening services have expanded as a result of the introduction of non-invasive nucleic acid amplification testing (NAAT). However, we do not know whether the natural history of NAAT detected infections is the same as culture detected infections. NAATs are 30–40% more sensitive than culture for detecting chlamydia,^2,3 and it is unknown whether NAAT positive/culture negative infections are as likely to progress to pelvic inflammatory disease (PID). Citing results by Scholes et al,⁴ Honey et al urge the conduct of further clinical trials to improve the accuracy and strength of evidence of the morbidity assumptions involved in CEA of chlamydia screening. The accuracy of this information is essential, as the probability of PID subsequent to untreated infection is central to the results and conclusions of a chlamydia screening cost effectiveness analysis. For example, Scholes’s analysis at the Seattle managed care organisation, which demonstrated that enhanced chlamydia screening reduced PID incidence, used enzyme immunoassay and culture technology—both of which are now becoming obsolete in clinical practice. If NAAT detectable, culture negative infections are not as transmissible, or do not progress to PID at a similar rate, increased testing and treatment costs would not be offset by increased benefit.

Economic modelling assumes rational behaviour on the part …