Epidemiologic analysis of a reported cancer cluster in a small rural population

This study investigated a reported cluster of cancer deaths in the small rural community of Bynum, North Carolina. Residents felt the proportion of deaths involving cancer had been increasing since the mid-1960s. To address this concern, cancer mortality was investigated from 1947 to 1985 to determine 1) if the proportion of cancer deaths had increased since the mid-1960s, 2) if it differed from what should be expected based on comparison with the reference population of the state of North Carolina, and 3) if observed mortality was within the bounds of statistical probability. Results indicated that the proportion of cancer deaths remained relatively constant from 1947 to 1964 (ranging from 9% to 14%) but increased steadily after 1965 to a high of 58% (1980-1985). Standardized proportionate mortality ratios adjusted for age, sex, race, and calendar time indicated that from 1975 to 1985 cancer deaths were 2.4 to 2.6 times greater than expected. Cancer mortality exceeded the upper limit of 95 percent Poisson confidence intervals from 1975 to 1985, which suggested that the excess proportion of cancer deaths was not likely to represent random case clustering. These findings serve to illustrate the feasibility of and a methodology for assessing reports of clusters in small populations.