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Giant African pouched rats (Cricetomys ansorgei) have been employed successfully in two operational
tuberculosis-detection projects in which they sniff sputum samples from symptomatic individuals who have
visited tuberculosis clinics. The prevalence of pulmonary tuberculosis in this population is high, approximately
20% in the regions where the rats have been used. If the rats are to be used to screen individuals from lower-
prevalence populations, their performance under such conditions must first be evaluated. In this study, the
prevalence of tuberculosis-positive samples presented to eight pouched rats was reduced to approximately 5%,
and the percentage of known-positive samples included as opportunities for reinforcement was varied in
sequence from 10 to 8, 6, 4, 2, 4, and 2. Liquid food reinforcers were delivered for identification responses to
known-positive samples and at no other time. The rats’ accuracy was clinically and statistically significantly
lower at 2% than at the other values. These results indicate that the rats can perform well in low-prevalence
scenarios but, if they are used under the conditions of the present study, at least 4% of the samples presented to
them must be opportunities for reinforcement. |
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