Space-time clustering of, and risk factors for, farmer-diagnosed winter dysentery in dairy cattle.

We used two statistical techniques for space-time cluster analysis, the Knox and the Mantel regression methods, for an analysis of whether herd outbreaks of farmer-diagnosed winter dysentery during the winter of 1987-1988 were clustered in space and time more than would be expected by chance. Using the Knox method, there was significant space-time clustering of outbreaks of winter dysentery within a 30 day time and a 5.5 km radius. There was also significant space-time clustering by the Mantel regression method.Logistic regression was used to study risk factors for herd outbreaks of winter dysentery. Large herds (>60 cows) and herds with a history of an outbreak prior to 1987 had increased chances of an outbreak occurring in 1987-1988.These results are compatible with an infectious cause for winter dysentery.