The Centers for Disease Control and Prevention (CDC) continues to be aware of the need for response to public concern as well as to state and local agency concern about cancer clusters. In 1990 the CDC published the "Guidelines for Investigating Clusters of Health Events," in which a four-stage process was presented. This document has provided a framework that most state health departments have adopted, with modifications pertaining to their specific situations, available resources, and philosophy concerning disease clusters. The purpose of this present article is not to revise the CDC guidelines; they retain their original usefulness and validity. However, in the past 15 years, multiple cluster studies as well as scientific and technologic developments have affected cluster science and response (improvements in cancer registries, a federal initiative in environmental public health tracking, refinement of biomarker technology, cluster identification using geographic information systems software, and the emergence of the Internet). Thus, we offer an addendum for use with the original document. Currently, to address both the needs of state health departments as well as public concern, the CDC now a) provides a centralized, coordinated response system for cancer cluster inquiries, b) supports an electronic cancer cluster listserver, c) maintains an informative web page, and d) provides support to states, ranging from laboratory analysis to epidemiologic assistance and expertise. Response to cancer clusters is appropriate public health action, and the CDC will continue to provide assistance, facilitate communication among states, and foster the development of new approaches in cluster science. Key words: cancer, cancer clusters, Centers for Disease Control and Prevention, environmental hazards, epidemiologic cluster investigations, state health departments. Environ Health Perspect 115:165-171 (2007). doi:10.1289/ehp.9021 available via http://dx.doi.org/ [Online 30 November 2006]
Disease clusters continue to concern the public, and public sentiment that environmental causes are responsible and must be investigated is widely prevalent. More than a decade ago, the Centers for Disease Control and Prevention (CDC) recognized the need to develop operating procedures for response to public concern about disease clusters. The National Conference on Clustering of Health Events was held 15-16 February 1989 in Atlanta, Georgia; the proceedings were published (Rothenberg et al. 1990a); and the CDC released the "Guidelines for Investigating Clusters of Health Events" (CDC 1990) in which a four-stage process was presented: a) an initial response to gather source information, b) an assessment of the occurrence of the health event, c) a feasibility study, and d) an epidemiologic investigation. During the last 15 years, these guidelines have provided a framework that most state health departments have adopted, modifying it for their specific situations and available resources. The states have the primary responsibility for response to cancer cluster concerns within their domain. The CDC guidelines emphasize the need for health agencies to develop an approach that maintains community relations while responding to clusters efficiently; the approaches vary among states as well as according to the nature of the cluster and the availability of case and comparison data. The orientation of each state-based inquiry response and investigation plan is shaped by state philosophy and experience with previous clusters.
The purpose of this article is not to revise the CDC guidelines; they retain their usefulness and validity. However, in the past 15 years, numerous cluster studies [Agency for Toxic Substances and Disease Registry (ATSDR) 2006; Cochise County Health Department (CCHD) 2005; Heath 2005; Massachusetts Department of Public Health (MDPH) 2005; National Cancer Institute (NCI) 2005; New Jersey Department of Health and Senior Services (NJDHSS) 2004; Rubin et al. 2007] as well as scientific and technologic developments have affected cluster science and response. Thus, we offer an addendum for use with the original document. Included in this list of significant developments are improvements in cancer registries, a federal initiative in environmental public health tracking (EPHT), refinement of biomarker technology, new cluster identification and geographic information systems (GIS) software, and the emergence of the Internet. These developments have shaped the approach of the CDC National Center for Environmental Health (NCEH) for public health response to cancer clusters.
Role of the CDC/NCEH in Cancer Cluster Response
Over the past several decades, industrialization and urban growth have increased human exposure to numerous toxic substances, and as a result, concern has been raised about their relationship to the etiology of chronic disease. The association between environmental factors and disease was validated in recent studies demonstrating that environmental factors such as tobacco smoke, toxic chemicals, dietary habits, and viral infections significantly increase the risk for several types of cancer (Lichtenstein et al. 2000; Thomas and Karagas 1996). A call for increased attention directed toward investigation of environmental exposure as a cause of chronic disease has been widely voiced in the media, the political establishment, and scientific forums.
NCEH defines a cancer cluster as a greater-than-expected number of cancer cases that occurs within a group of people in a geographic area over a defined period of time. In 2000, representatives from the CDC Division of Cancer Prevention and Control (DCPC), National Institute for Occupational Safety and Health (NIOSH), ATSDR, and NCEH met and recognized the importance of a centrally coordinated cancer cluster response to inquiries within the CDC. They assigned this responsibility to NCEH. The rationale for this decision was the strong public perception that environmental exposures are directly responsible for cancer. NCEH now provides a centralized coordinated response system for cancer cluster inquiries received by the CDC. Since the inception of this new responsibility, NCEH has initiated several cluster-related activities (Table 1).
Cancer Cluster Public Inquiry Triage System. In 2002, NCEH initiated a centralized inquiry system within the CDC, the Cancer Cluster Public Inquiry Triage System (CCPITS; CDC 2004) for responding to cancer cluster inquiries from various audiences such as individual citizens, state health departments, and other federal agencies (Figure 1). The goals of the system are to a) provide individual, targeted responses to the public in a timely manner, b) decrease the chances of an inquirer having to contact multiple agencies, and c) increase communication about cancer clusters among the participating agencies. The response from NCEH to individuals includes basic information on cancer clusters, response to the specific cancer cluster concern, referral to the appropriate state health department and state cancer registry contacts, and links to additional information. NCEH also notifies the state contacts of the inquiry and response. The NCEH cancer cluster website (http://www.cdc.gov/nceh/clusters; CDC 2004) was developed and designed to support the inquiry system and to facilitate information sharing among federal, state, and local agencies; it provides the cornerstone for the cancer cluster inquiry system. If the inquiry concerns a hazardous waste site, work site, or basic cancer issue, NCEH triages the inquiry to ATSDR, CDC/NIOSH, or DCPC, respectively. NCEH tracks inquiry information via an ACCESS database (Microsoft Corp., Redmond, WA) and communication among CDC programs, federal, state, and local agencies is improved as a result of this single point of contact. Since the inception of the system through July 2005, the cancers of concern most frequently cited by inquirers were …