Evidence for clustering of amyotrophic lateral sclerosis in Wisconsin.

Clustering of amyotrophic lateral sclerosis (ALS) occurs in the western Pacific, but has not been convincingly demonstrated for the sporadic form of the disease which occurs throughout the rest of the world. Using death certificate data we identified 529 ALS-associated deaths in Wisconsin during the interval 1973-82, representing a statewide mortality rate of 1.12 deaths/100,000/yr. Using computer simulation we show that cases were not homogeneously distributed throughout the population and that there exists a significant cluster of cases in northeastern Wisconsin.