Spatial and temporal clustering of an occupational poisoning: the example of green tobacco sickness

Nicotine poisonings in tobacco farm workers (Green Tobacco Sickness, GTS) reported to the Kentucky Regional Poison Center during 1991 were assessed for spatial, temporal and space-time clustering. Among 62 index cases, 10 had worked with others who also reported GTS that day. Analysis of index cases, using Best and Rayner's V(2), showed significant cyclic clustering by hour of day the report was received (p = 9 x 10(-9)); chi-square revealed significant spatial clustering by agricultural district (p = 0.0002). Space-time clustering was detected using the E-M-M statistic (p = 0.008); however, the space-by-time interaction of Rao's chi-square goodness-of-fit statistic did not detect space-time clustering (p = 0.32).