Bayesian estimation of test characteristics of novel molecular microarray assay and bacteriological culture for diagnosis of Mycoplasma californicum mastitis using latent class analysis.

Accurate diagnosis of Mycoplasma californicum (M. californicum) infection remains a major challenge in dairy herds due to intermittent shedding patterns and the inherent limitations of conventional bacterial culture. Therefore, development of new diagnostics with improved accuracy is critical for timely intervention and proper herd management; as Mycoplasma mastitis can spread rapidly through a herd if not properly identified and controlled. The objective of this field study was to estimate test characteristics of molecular microarray assay (MMA) and bacterial culture for diagnosis of bovine mastitis with M. californicum using Bayesian latent class analysis (BLCA) to avoid the assumption of a perfect reference test. A total of 955 milk samples were collected from two dairy herds in California, USA. Milk samples were collected because of sharp decrease in milk yield and increase of cow-level and bulk tank-level somatic cell counts and submitted for laboratory examination. Two-tests-two-populations BLCA model was fit to estimate sensitivity and specificity of both tests. Our findings showed that MMA has a higher sensitivity compared to bacterial culture with an estimate of 83% (95% PPI: 76.9-88.05) whereas the sensitivity of bacterial culture was 60% (95% PPI: 54.05-65.97). The specificity estimates of MMA and bacterial culture were very high and similar, and both specificities were always above 99%. The apparent prevalence of M. californicum based on bacterial culture was 22% (210/955). The estimated prevalence of M. californicum was high, and markedly different where it was 67% (95% PPI: 60.54-72.52) and 18.25% (95% PPI: 14.82-21.95) in first and second populations, respectively. The estimated prevalence of M. californicum indicates the underestimation of M. californicum infection in the examined herd populations. In conclusion, the high diagnostic performance of MMA lends its usefulness as a routine test for accurate diagnosis of M. californicum mastitis in dairy cattle. The use of MMA for diagnosis of M. californicum mastitis provides reliable, timely interventions compared to traditional culture, which could limit the infection spread in the dairy herd and eventually reduce economic losses. BLCA proposes a useful and unique alternative to classic test evaluation of diagnostic tests used for diagnosis of M. californicum mastitis in dairy herds.