Cluster Investigation Analysis

Disease clusters are aggregations of cases of a specific disease in space and/or time, in a community or an occupational group, at a level greater than expected by chance. Co-occurrences of cases are commonplace, and such occurrences are frequently reported as potential clusters. Various exposures in the environment, community, or workplace are frequently suggested as potential sources of potential clusters. However, co-occurrences of disease cases are not necessarily clusters. Often straightforward, preliminary analyses can resolve the question of whether a cluster exists. However, in some circumstances a comprehensive epidemiological, statistical, and exposure investigation may be required to confirm whether a true cluster exists and could be related to some type of environmental or occupational exposure.

Exponent’s epidemiologists, biostatisticians, industrial hygienists, and environmental scientists have the expertise required to analyze disease clusters and have been directly involved in numerous disease clusters investigations. Our teams of scientists have evaluated reports of increased occurrences of disease in the workplace, community, and environment. We have conducted epidemiologic investigations to assess potential workplace and community cancer clusters, and we have provided consulting regarding potential clusters of reproductive outcomes such as birth defects or spontaneous abortions.

Our staff can apply state-of-the-art mapping and statistical tools to characterize the spatial patterns of disease occurrence. 

Our investigations typically address the following types of questions: 

  • Are the rates of disease greater than expected in person, place, and time? 
  • If the observed rates of disease are greater than expected, is there documented exposure that could explain this cluster? 
  • Does the proposed exposure reflect a biologically plausible relationship between exposure and disease? 
  • Are there alternative explanations for the perceived cluster of disease? 
  • Are there specific sub-groups that may or may not be at an elevated risk of disease? 
  • Are improvements needed in the workplace or environmental health surveillance systems to accurately characterize potential clusters? 

It is often necessary for disease cluster investigations (including those that are potentially related to environmental or occupational exposures) to be conducted—and the results of these investigations be communicated—amid heightened public concerns and attention. Public health agencies, industrial facility management, and other stakeholders must strike a balance in addressing community concerns and in conducting the appropriate level of scientific study. Exponent health scientists can help to identify the appropriate scientific approach, implement relevant data collection, analyze available health data and communicate study findings to stakeholders.

Publications/Reports – Disease Cluster Evaluations 

Moolgavkar SH, Chang ET, Watson H, Lau EC. Cancer mortality and quantitative oil production in the Amazon region of Ecuador, 1990–2010. Cancer Causes Control. 2014; 25 (1): 59-72.