Investigating disease clusters: why, when and how?

The investigation of disease clusters, aggregations of a few to several cases of disease, remains a controversial issue in epidemiology and public health. Reported at the rate of more than three per day nationally, a response commands substantial resources. This paper considers whether scientists or public health officials should investigate disease clusters, when they should, and, if so, how. Part of the disparity in opinions arises from differing goals: trying to identify new carcinogens versus identifying situations in which people are at risk. There are also differences in investigation strategies: passive versus active. This paper suggests that a more active surveillance programme with occasional investigation may best meet the needs of the public while accommodating the limited resources of public health officials and some of the concerns of epidemiologists.