Setting. Tanzania. Objective. To compare microscopy as conducted in direct observation of treatment, short course centers to pouched rats as detectors of Mycobacterium tuberculosis. Design. Ten pouched rats were trained to detect tuberculosis in sputum using operant conditioning techniques. The rats evaluated 910 samples previously evaluated by smear microscopy. All samples were also evaluated through culturing and multiplex polymerase chain reaction was performed on culture growths to classify the bacteria. Results. The patientwise sensitivity of microscopy was 58.0%, and the patient-wise specificity was 97.3%. Used as a group of 10 with a cutoff (defined as the number of rat indications to classify a sample as positive for Mycobacterium tuberculosis) of 1, the rats increased new case detection by 46.8% relative to microscopy alone. The average samplewise sensitivity of the individual rats was 68.4% (range 61.1–73.8%), and the mean specificity was 87.3% (range 84.7–90.3%). Conclusion. These results suggest that pouched rats are a valuable adjunct to, and may be a viable substitute for, sputum smear microscopy as a tuberculosis diagnostic in resource-poor countries. 1. Introduction A major hurdle in combating tuberculosis (TB) is diagnosing the disease in resource-poor countries.Sputum smear microscopy, the technique typically used, is relatively slow and characteristically has high specificity but low sensitivity [1, 2]; therefore, the international medical community has prioritized developing a quick, accurate, and affordable alternative diagnostic. In an attempt to develop one, researchers recently have investigated the use of scent-detecting pouched rats (Cricetomys gambianus) as a TB diagnostic.An initial proof of principle investigation [3] revealed that pouched rats trained through operant conditioning procedures could detect TB in human sputum, and three subsequent studies, involving a total of over 20,000 patients, showed that using the rats in second-line screening of sputum samples initially screened by smear microscopy at direct observation of treatment—short course (DOTS) centers in Tanzania increased new case detections by 31.4% [4], 44% [5], and 42.8% [6]. These results are promising, but the accuracy of Cricetomys in detecting TB has not been extensively evaluated relative to an established reference standard. Culturing is considered the “gold standard” for TB detection [2], and Weetjens et al. [3] reported the results of a study in which two rats, Mandela and Kingston, evaluated 817 sputum samples also evaluated by culturing, which
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