Families Against Cancer & Toxics

(Developed by the Trust for America's Heath)



Cluster Request Process

The following process describes the Centers for Disease Control and Prevention's (CDC) guidelines for responding to disease cluster investigation requests. Some state health departments may follow their own protocol for responding to disease cluster investigation requests.

1. You suspect a chronic disease cluster in your community.
According to the Centers for Disease Control and Prevention (CDC) a cluster is "an aggregation of cases of a disease or other health condition that are closely grouped in time and place. The number of cases may or may not exceed the number expected, and frequently the expected number is not known." Among chronic diseases, cancer and birth defects cases have been investigated as clusters.


2. Contact the local health department.
If your city, county, town or district has a health department, it can probably be found in the Blue Pages of your local phone book. These health departments may be divisions of the state health department or separate entities. The priority of most local health departments is to protect, promote and maintain health at the community level.


3. Contact the state health department.
From Council of State and Territorial Epidemiologists, visit www.cste.org


4. Health department should gather information (in some instances, may be mostly information you provide). Examples of information health department may request are the following:
a. The suspected health event (e.g., cancer, birth defect, etc.)
b. The number of cases
c. Suspected exposure(s) (e.g., environmental, etc.)
d. Geographic area of concern
e. Time period of concern
f. Identifying information on persons affected (e.g., name, gender, diagnosis, length of time at residence of concern, etc.)


5. Health department should send you information:
a. Summary report of your request will include the information you related to health department.
b. General information about clusters will include information regarding factors that define clusters.


6. "Preliminary evaluation:" HD should assess if excess number of cases exists
a. Purpose is to provide a rough estimate of the chance that the event has occurred
b. Phase entails using the data obtained in previous phases to determine actual (observed) versus calculated (expected) number of cases.
c. If there is NOT a greater number of cases than expected, HD will inform you of the results to date indicating that further investigation is unnecessary.
d. If there IS a greater number of cases than expected OR that there is a biologic or public health concern, the investigation proceeds to the next phase.


7. "Case evaluation:" HD should assess if biological basis exists
a. Purpose is to confirm the diagnosis.
b. Phase entails communicating with physicians, pathology labs, and/or the appropriate disease registry.
c. If the diagnoses are NOT confirmed, HD will inform you of the results to date indicating that further investigation is unnecessary.
d. If the diagnoses ARE confirmed and there is an excess number of cases OR there is biologic plausibility, the investigation proceeds to the next phase.


8. "Occurrence evaluation:" HD should obtain more detailed description of the cluster
a. Purpose is to plan and carry out a field investigation to determine if there is an excess occurrence of cases as well as to elucidate the characteristics of this occurrence.
b. Phase entails determining the geographic and temporal boundaries; obtaining all potential cases; assessing potential exposures or risk factors; performing detailed reviews of the literature and using data from relevant databases and community members.
c. If an excess number of cases is NOT found, HD will inform you of the results to date indicating that further investigation is unnecessary.
d. If an excess number of cases IS confirmed, but there is NO confirmed link to any exposure, HD will inform you of the results to date and advise you of any potential risks.
e. If an excess number of cases IS confirmed, AND there is biologic plausibility, the investigation proceeds to the next phase.


9. "Major feasibility study:" HD should determine if carrying out an epidemiologic study linking the disease/health event and potential exposure(s) is reasonable
a. Purpose is to determine the likelihood of an epidemiologic study identifying a link between the cases and suspected risk factor/exposure.
b. Phase entails reviewing literature; assessing potential study costs; determining appropriate data collection and analysis; and identifying potential social, political, and policy implications of the proposed study and findings.
c. If the feasibility study shows little likelihood of finding a link between disease and exposure(s), HD will inform you of the results to date indicating that further investigation is unnecessary.
d. If the study shows that there IS a likelihood of finding a link between disease and exposure(s), the investigation proceeds to the last phase.


10. "Etiologic investigation:" HD should conduct study to determine potential link between disease/health event and exposure(s)
a. Purpose is to conduct a study of the potential link between disease/health event and exposure(s)
b. Results of the study expected to add to public health knowledge.