Accuracy of Tests for Diagnosis of Animal Tuberculosis: Moving Away from the Golden Calf (and towards Bayesian Models)

Abstract

The last decades have seen major efforts to develop new and improved tools to maximize our ability to detect tuberculosis-infected animals and advance towards the objective of disease control and ultimately eradication. Nevertheless, there is still uncertainty regarding test performance due to the wide range of specificity and especially sensitivity estimates published in the scientific literature. Here, we performed a systematic review of the literature on studies that evaluated the performance of tuberculosis diagnostic tests used in animals through Bayesian Latent Class Models (BLCMs), which do not require the application of a (fallible) reference procedure to classify animals as infected with tuberculosis or not. BLCM-based sensitivity and specificity estimates deviated from those obtained using a reference procedure for certain antemortem tests: an overall lower sensitivity of skin tests and serology and a higher sensitivity of interferon-gamma (IFN-γ) assays was reported. In the case of postmortem diagnostic tests, sensitivity estimates from BLCMs were similar to estimates from studies based on other methodologies. For specificity, the range of BLCM-based estimates was narrower than those based on a reference test, reaching values close to 100% (but lower in the case of IFN-γ assays). In conclusion, Bayesian methods have been increasingly applied for the evaluation of tuberculosis diagnostic tests in animals, yielding results that differ (sometimes substantially) from previously reported test performance in the literature, particularly for in vivo tests and sensitivity estimates. Newly developed models that allow adjustment for relevant factors (e.g., age, breed, region, and herd size) can contribute to the generation of more unbiased estimates of test performance. Nevertheless, although BLCMs for tuberculosis do not require the use of an imperfect reference procedure and are therefore not influenced by its limited performance, they require careful implementation, and transparent systematic reporting should be the norm.

Figure 1

Flow of information followed during the systematic review process.

Figure 2

95% posterior probability intervals for the sensitivity and specificity estimates obtained for antemortem tests in the studies retrieved in this study.

Figure 3

95% posterior probability intervals for the sensitivity and specificity estimates obtained for postmortem tests in the studies retrieved in this study.

Figure 4

Scatterplots of 95% prior and posterior interval widths for sensitivity (a) and specificity (b) of diagnostic tests for tuberculosis in studies that used informative prior distributions.

Figure 5

Combined prior and posterior distributions of sensitivity and specificity estimates of antemortem diagnostic tests for tuberculosis obtained using informative priors (left: sensitivities; right: specificities). Each trial was set to have the same weight. This information is shown by trial in Supplementary Material 3.

Figure 6

Combined prior and posterior distributions of sensitivity and specificity estimates of postmortem diagnostic tests for tuberculosis obtained using informative priors (left: sensitivities; right: specificities). Each trial was set to have the same weight. This information is shown by trial in Supplementary Material 3.

Figure 7

Results of the STARD-BLCM checklist review by the authors. NA refers to articles where the item was not applicable.