An analysis of disease surveillance data that uses the geographic locations of the reporting units.

The primary purpose of a disease surveillance system is to provide data for the detection of changes in the incidence of the disease. Methods for the analysis of data from surveillance systems are reviewed. A new procedure is proposed for use when the system includes geographically dispersed reporting units, such as hospitals or administrative regions. The method is based on the cusum statistic, and combines information from different units according to their geographic relationships.