Agency for Toxic Substances and Disease Registry Case Studies in Environmental Medicine (CSEM)
Disease Clusters: An Overview
Case Confirmation
Once a case definition has been selected, it is then necessary to confirm that those "cases" that defined the "cluster" really exist. It is essential to confirm that all cases share some clearly defined set of symptoms, physical findings, radiographic findings, and/or laboratory findings. The relevant importance of each type of information might vary depending on the specific disease of concern, but the need for case confirmation remains constant. The public health department's role is to determine and validate that the reported cases actually meet the case definition.
Many apparent clusters disappear at this stage of the cluster evaluation. In some cases, it might be discovered that an apparent cluster is actually an assortment of unrelated diseases and disease processes. For example, a "brain cancer cluster" might actually be found to include patients with metastases from distant sites, patients with nonneoplastic infiltrative diseases, and even patients who have suffered strokes. Other clusters might eventually be found to represent nothing but a random pattern of incorrectly reported laboratory results or clinical findings, or might reflect coding problems in hospital discharge summaries.
