Dynamics of Escherichia coli O157:H7 outbreak detection and investigation, Minnesota 2000-2008

We determined characteristics of Escherichia coli O157:H7 pulsed-field gel electrophoresis clusters that predict their being solved (i.e. that result in identification of a confirmed outbreak). Clusters were investigated by the Minnesota Department of Health (MDH) using a dynamic iterative model. During 2000-2008, 19 (23%) of 84 clusters were solved. Clusters of ≥3 isolates were more likely to be solved than clusters of two isolates. Clusters in which the first two case isolates were received at MDH on the same day were more likely to be solved than were clusters in which the first two case isolates were received over ≥8 days. Investigation of clusters of ≥3 E. coli O157:H7 cases increased the success of cluster investigations.