Agency for Toxic Substances and Disease Registry Case Studies in Environmental Medicine (CSEM)
Disease Clusters: An Overview Develop Biologically Plausible Hypotheses
On completion of the exposure assessment, the public health department will decide whether the available information is sufficient to generate a biologically plausible hypothesis to explain the cluster.
To generate a biologically plausible hypothesis, the public health department conducts structured interviews with each affected individual. By means of standardized, structured questionnaires, each patient is asked about medical history, family history, work history, hobbies and other activities, lifestyle, historical exposures, and risks of exposures. Some cluster investigations also delve into acquaintanceship patterns. The interview results are carefully reviewed in an effort to find patterns suggesting possible similarities linking the affected cases that can form the basis of exposure hypotheses. Once common factors are identified among the cases, a comparison of the affected individuals to randomly selected groups of others from the denominator population can then test the significance of such patterns.
Biologic plausibility might also depend on whether there is evidence of shared exposure to a chemical capable of causing the disease of concern, whether the exposures had been of sufficient magnitude to cause adverse effects, and whether all affected individuals had been exposed. Additionally, the temporal relationship between exposure and effect should be evaluated in terms of what information is known. Many diseases such as cancers develop only after a delay (or latency period) lasting years or, more often, decades. (Latency period is the duration of time from first exposure to first symptoms or signs of a disease.) For that reason, it would not be biologically plausible to link very recent exposure to the onset of cancer.
Clinicians in communities affected by disease clusters have an important role in understanding and translating the science of cluster investigations and an equally important role in reporting possible disease clusters to the local public health units in their practice communities.
The physician's responsibility is to
Suspect a cluster of disease based on clinical observation.
Complete an exposure history.
Confirm case(s) through accurate clinical and laboratory diagnosis.
Act as a sentinel in reporting cases to the local public health department.
Educate patients about occurrence of disease.
The first line for contact is the public health department. The public health department can initiate
