Evaluation of the sensitivity and specificity of three diagnostic tests for Coxiella burnetii infection in cattle and buffaloes in Punjab (India) using Bayesian latent class analysis

Q Fever is a zoonotic disease of significant animal and public health concern, caused by Coxiella burnetii (C. burnetii) , an obligate intracellular bacterium. This study was done to evaluate the sensitivity ( Se ) and specificity ( Sp ) of three diagnostic methods to diagnose C. burnetii infection in cattle and buffaloes in Punjab, India: an indirect ELISA method applied in serum samples and a trans-Polymerase Chain Reaction (trans-PCR) technique applied in milk samples and genital swabs. Bayesian Latent Class Models were developed following the STARD-BLCM reporting guidelines. Conditional independence was assumed between the tests, given (i) the different biological principle of ELISA and trans-PCR and (ii) the fact that the trans-PCR was performed on different tissues. The ELISA method in the serum samples showed the highest Se of 0.97 (95% Probability Intervals (PIs): 0.93; 0.99) compared to the trans-PCR method applied in milk samples 0.76 (0.62; 0.87) and genital swabs 0.7 (0.55; 0.82). The Sps of all tests were high, with trans-PCR in genital swabs recording the highest Sp of 0.99 (0.98; 1), while the Sp of trans-PCR in milk samples and ELISA in serum samples were 0.98 (0.96; 0.99) and 0.95 (0.93; 0.97) respectively. The study results show that none of the applied tests are perfect, therefore, a testing regimen based on the diagnostic characteristic of the tests may be considered for diagnosis of C. burnetii .