We categorized individuals into ''extreme'' and ''normal'' expression groups (as above) and scanned for temporal clusters of extreme expression using a Bernoulli model in the programme SaTScan TM . A significant temporal cluster (cluster 1) was detected in late June 2008 (log likelihood ratio = 20.37, P = 0.001). Adjusting for the occurrence of the most significant cluster, a significant secondary temporal cluster (cluster 2) occurred in early September 2008 (log likelihood ratio = 13.10, P = 0.001). Analyses for spatial clusters and spatial-temporal clusters failed to detect any purely spatial clustering, but did find two significant space-time clusters (P = 0.014) within the time frame of the most significant temporal cluster. The areas included and not included in these clusters appeared to broadly correspond to distinct forestry blocks.