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Screening of asymptomatic Chlamydia trachomatis (CT) infections is indicated to prevent the spread of CT and the development of secondary complications like pelvic inflammatory disease, ectopic pregnancy, and tubal infertility. Cost effectiveness presents an important aspect in the decision making regarding actual implementation. A recent paper in this journal by Van Valkengoed et al1 addressed cost effectiveness, using an established pharmacoeconomic model,2 of a systematic screening programme for asymptomatic CT infections in women registered in general practices in Amsterdam, based on mailed home obtained urine specimens.3 The aim of this letter is to extend the application of the pharmacoeconomic model with regard to pooling and improved test performances (sensitivity and specificity).
We recently determined the sensitivity and specificity for two commercially available CT detection assays for urine specimens from asymptomatically CT infected women and men.4 In total, 2906 mailed home obtained urine specimens were tested for CT using both ligase chain reaction (LCR) and polymerase chain reaction (PCR) testing. We showed that for individual testing, the test sensitivity/specificity for LCR and PCR could be estimated at 78.6%/99.7% and 98.8%/99.9%, respectively. Furthermore, we recently showed by using individual urine samples (n = 650) and samples pooled by five (n =130) that pooling has a relative sensitivity and specificity of 100%. Since only CT positive pools have to be analysed for the individual CT positive cases approximately 60% of the number of tests could be saved in our population with an estimated CT prevalence of 2–3%.5
In the pharmacoeconomic model test performances of 85.0% sensitivity and 99.0% specificity were previously assumed.1 Furthermore, the model included population based estimates of CT prevalence, the costs of the programme, the health gain effects and the related monetary benefits. Health gain effects considered were averted pelvic inflammatory disease, chronic pelvic pain, ectopic pregnancy, infertility, and neonatal pneumonia (major outcomes averted; MOA). Both direct and indirect costs and benefits were considered. We investigated the effects on baseline cost effectiveness of pooling and improvements in test performance.
Population based prevalence in the systematic screening was 2.2% for women aged 15–40 and 2.9% for women aged 15–25. Van Valkengoed et al estimated baseline cost effectiveness for systematic screening in Amsterdam using LCR at net costs of US$11 100 for women aged 15–25 and $15 800 per MOA for women aged 15–40 (table 1).1 High performance testing of 98.8% sensitivity and 99.9% specificity was estimated to reduce net cost per MOA by approximately 20%. Pooling urine specimens by five was estimated to reduce net costs per MOA by 57%. A total decrease of 67% was estimated if both high performance testing and pooling are assumed (table 1).
We conclude that with pooling and application of high performance testing major improvements in cost effectiveness of screening women for asymptomatic CT can be obtained.
This work was partly supported by ZON (Prevention Fund), grants 28-1181-1 and 28-2705. The authors acknowledge the assistance and cooperation of all researchers, physicians, nurses, and participants involved in the project on systematic screening for Chlamydia trachomatis in Amsterdam.