Investigation of a bladder cancer cluster in northwestern Illinois.

Cancer maps from 1950 through 1979 revealed areas of high mortality from bladder cancer for both males and females in several northwestern Illinois counties. In order to further explore this excess, a bladder cancer incidence study was conducted in the eight counties comprising this region. Eligible cases were those first diagnosed with bladder cancer between 1978 and 1985. Age adjusted standardized incidence ratios were calculated for each county and for 97 zip codes within these counties. County results revealed no excesses. Zip code results indicated elevated risks in a few areas, but only two zip codes had significantly elevated results. One of these zip codes had a significant excess in males (standardized incidence ratio = 1.5) and females (standardized incidence ratio = 1.9). This excess was primarily confined to one town in this zip code, in which standardized incidence ratios were significantly elevated in males (1.7) and females (2.6). Further investigation revealed that one of four public drinking water wells in this town had been closed due to contamination; two wells were within a half mile (0.8 km) of a landfill site that had ceased operating in 1972. Tests of these two wells revealed traces of trichloroethylene, tetrachloroethylene, and other solvents. Further investigation of this cluster is discussed.