391 dairy herds, stratified for size and province, were selected with the purpose of estimating paratuberculosis herd prevalence in the Lombardia region, a Northern Italian Region where 15.000 dairy herds and 45% of the national milk production are concentrated. The prevalence of infected herds was estimated by a commercial ELISA test (Institut Pourquier) on individual blood samples of 38.487 dairy cattle over 12 months. The percentage of herds showing at least one seropositive animal was 43.7%, while the percentage of seropositive cows was 2.6%. On the basis of the performances of ELISA test on blood (sensititity 45%, specificity 99%), the herds that didn't reach a herd specificity of 95% were tested for confirmation by fecal culture on the seropositive cows.

The resulting estimated herd prevalence was 19.2%.