Analysis of spatial and temporal clustering of horses with Salmonella krefeld in an intensive care unit of a veterinary hospital

Objective - To determine whether clustering existed in the spatial or temporal distribution of horses that shed Salmonella krefeld in their feces during hospitalization. Design - Retrospective analysis of medical records. Animals - 219 horses housed in the intensive care unit of a veterinary medical teaching hospital from October 1991 through May 1992. Procedure - Bacteriologic culturing of fecal samples was used to identify horses shedding S krefeld. For affected horses, the scan statistic was used to analyze temporal clustering, and Knox's method was used to analyze temporal-spatial clustering. Results - 20 horses were identified as shedding S krefeld in their feces. Significant temporal clustering of affected horses was observed for periods of 5, 6, 7, and 8 days. Temporal-spatial analysis did not detect a significant distribution for any combination of time and distance among affected horses. Clinical Implications - Detection of temporal clustering and concurrent random temporal-spatial distribution of affected horses suggested that affected horses were grouped in time, but means of transmission was not related to proximity between horses.