Reliability of environmental sampling to quantify Mycobacterium avium subspecies paratuberculosis on California free-stall dairies

Schematic presentation of a longitudinal study of the reliability of environmental sampling and testing methods to quantify Mycobacterium avium ssp. paratuberculosis in cow pens in 4 California free-stall dairies. Pens were nested within dairy and crossed with collector and day of sampling.

Bland and Altman plots of the differences in results of environmental samples collected simultaneously by 2 collectors and tested for Mycobacterium avium ssp. paratuberculosis by A) quantitative real-time PCR in duplicate and reported as mean cycles-tothreshold (Ct), and B) Herrold's egg yolk medium culture in 4 tubes with mycobactin and reported as natural log (ln) transformation of the mean colony-forming units (cfu) per tube. The solid and dashed lines represent the mean of the differences and 95% limits of agreement between the 2 collectors, respectively.