The Rapid Test Paradox: When Fewer Cases Detected Lead to More Cases Treated

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Abstract
Background and Objectives: Screening tests for detection ofChlamydia trachomatisinclude those processed in laboratories and those designed to be processed at the point of care. The latter tests can yield results at the time of the initial patient visit, but most available lab-processed tests have greater sensitivity. In settings where a proportion of patients do not return for treatment after positive test results, the less sensitive rapid tests could lead to the treatment of more patients and be more cost-effective. Goal of this Study: To determine the situations, if any, in which a rapid test might be more cost-effective and treat more infections than lab-based tests. Study Design: A decision analysis framework was used to compare one point-of-care test (the BioStar Chlamydia OIA) with two lab-based tests (cell culture and the polymerase chain reaction [PCR] assay). It was assumed that all women in the model would be screened. Variables included in the analysis were the prevalence, test sensitivity and specificity, the probability of developing pelvic inflammatory disease after treated and untreated chlamydial infections, and the likelihood that patients would wait for rapid test results or return to the facility for treatment. Results: The rapid test treated more cases of infection than the PCR alone if the return rate was less than 65%. A two-test algorithm of the rapid test followed by a PCR test on those initially testing negative identified and treated the greatest number of chlamydial infections and was the most cost-effective at all prevalences above 9%, but this finding was sensitive to the cost estimate for pelvic inflammatory disease. Conclusion: In settings where patient return for treatment is a problem, point-of-care tests contribute significantly to the detection and treatment of chlamydial infections among women.