(A) Relative risk estimates of sporadic STEC infection across New Zealand and (B) cattle density from 2011. (A) The bivariate kernel density plot shows estimates of relative risks of STEC infection across regions in New Zealand. Values >0 on the relative risk scale indicate increased risk of infection. (B) Total cattle density (dairy and beef animals/km2) from 2011 is shown to indicate areas with high cattle densities. Similar plots of the densities of dairy, beef, sheep, and deer are provided in the supplementary material (Additional file 2).