It is well known that short-term, high-level exposures to environmental chemicals can cause adverse health effects. Much of what is known about these types of exposures is based on occupational exposure research involving individuals or small groups of people who have been potentially exposed to environmental chemicals. However, less is known about the effects that long-term low-dose exposures can have on people's health, particularly when the potentially exposed population is large. Health effects such as birth defects, developmental disorders, neurological and immunological diseases, and cancer are often attributed to environmental exposures. When the suspected exposure source is found in a specific location, or community in a higher number than would be expected when compared to comparable locations, people in the community become concerned that there is a disease "cluster". Furthermore, people are also worried that something in their environment is causing the cluster.
Disease clusters, such as cancer clusters, can have a devastating impact on individuals, families, and communities. From a public health perspective, the "perception" of a cluster in a community may be as important as, or more important than, an actual cluster. Public concern increases quickly when people think there is a cancer cluster in their community and that they and/or their children will be harmed. These situations deserve prompt and effective public health attention.
In the public's mind, cancer clusters are caused by something in the environment until proven otherwise. While certain clusters may result from environmental exposures, we need to consider many possible explanations before drawing conclusions. When searching for the cause of a cancer cluster, public health workers will have the opportunity to review the unique environmental aspects of a community and identify existing known environmental hazards. If public health workers identify a public health hazard, they should quickly remedy the situation. Public health action to remove a known human health hazard should not be delayed.
Cancer cluster reports are common because cancer is common. The American Cancer Society predicts that this year 1,220,000 Americans will be diagnosed with non-dermatologic cancer; and over 553,000 Americans will die this year because of all types of cancer. Fortunately, we are making progress in preventing and controlling cancer. CDC recently reported good news from California where lung cancer incidence fell 14 percent between 1988 and 1997. The reported decline may be related, in part, to the significant declines in smoking rates as a result of California tobacco control programs. We also know that early detection of cancer through cancer screenings saves lives. But, the preventible causes of many cancers remain elusive.
I can assure you that CDC and Agency for Toxic Substances and Disease Registry (ATSDR) are committed to a public health system that can quickly identify and respond to community concerns about cancer clusters. Cancer cluster activities must be integrated into the broader public health approach to cancer prevention and environmental hazard control. A community suspects that a cancer cluster exists when more cases of cancer have occurred than are expected and when there is a possibility that the cases share a common cause. A few cancer cluster investigations have led to the discovery of preventable causes, but this is the exception rather than the rule. These investigations involved astute researchers and physicians who identified an excess of extraordinarily rare cancers among their patients (e.g.; adenocarcinoma of the vagina and diethylstilbestrol; Kaposi's sarcoma and HIV virus; liver angiosarcoma and vinyl chloride monomer) or who identified a cluster of certain cancers known to have a single preventable cause (e.g.; mesothelioma and asbestos).
Approximately 85 to 90 percent of investigations of suspected cancer clusters find no increased cancer incidence. Even though 10 to 15 percent of investigated clusters do show that the study population has a higher than expected cancer risk, this increased risk, may be due to the random distribution of cancer within a population (i.e. chance). The causes of the remaining clusters are unknown. Routine analysis of cancer registry data to identify cancer clusters can increase the number of chance clusters. Statistical tests of cancer registry data cannot separate observed clusters caused by chance from those due to an unrecognized common cause.
Although cancer clusters rarely provide a scientific opportunity to identify a new cause of cancer, public health agencies require the capacity and technical expertise to support a staged response to public inquiries about cancer clusters. Public health agencies require the scientific and technical expertise to identify when an excess cancer has occurred and to reassure communities when it does not. Cancer clusters are reported throughout the United States. A survey by the Council of State and Territorial Epidemiologists found that 41 state health departments reported 1,900 cancer inquiries in 1996. We don't know the total number of reported cancer clusters because there is no national tracking system to identify suspected or confirmed clusters.
Measuring Environmental Exposures
Our challenge is to address the public's fear that something in their "environment" is causing the cluster. To effectively determine the public health impact of a chronic environmental exposure, three things are tracked. First, we cannot know the hazards of chemicals in humans unless we monitor what chemicals actually are in the environment. Tracking toxic chemicals in the environment must include the amount, concentration, and geographic distribution of known and potential toxic chemicals. Some systems for tracking this type of data already exists, for example, within the U.S. Environmental Protection Agency's (EPA) Toxic Release Inventory which collects data down to the local level. There are also EPA and state data bases for water, air, and pesticide environmental contaminants.
Second, actual human exposure levels are tracked through measurement of chemicals in human blood and urine through a process known as "biomonitoring." CDC released the first annual National Report on Human Exposure to Environmental Chemicals. This first edition of the Report presents levels of 27 environmental chemicals measured in the U.S. population. These chemicals include metals (e.g., lead, mercury, and uranium), cotinine (a marker of environmental tobacco smoke exposure), organophosphate pesticide metabolites, and phthalate metabolites. An example of what we have observed so far is a decline from 71 percent in the early1990's to 32 percent in1999 for non-smoking Americans exposed to environmental tobacco smoke. We are expanding the Report to include 100 environmental chemicals. Chemicals under consideration for future Reports include carcinogenic volatile organic compounds, carcinogenic polyaromatic hydrocarbons, dioxins, furans, polychlorinated biphenyls, trihalomethanes, haloacetic acids, carbamate pesticides, and organochlorine pesticides. This data will be collected annually and the number of chemicals tracked will increase, but this data is currently only available on a national level.
Finally, health outcomes are to be tracked over time. Specifically, both disease events and trends in health risk behavior need to be monitored over time through tracking systems such as vital statistics, health surveys, and disease registries. As we build a comprehensive disease tracking system in the U.S. that can provide data on a range of chronic conditions at the national, state, and local levels, it will be designed so that the data collected can be linked to the data from the other two tracking components. A comprehensive, nationwide exposure and disease tracking system is the only means to access the magnitude and nature of health risks from environmental exposures.
A Staged Response to Clusters
I will now describe the components of a staged response to clusters which includes the multi-level, multi-agency public health response that is required to address potential health problems and public concerns related to potential environmental exposures.
The State Role
Cancer cluster concerns should be addressed by state health departments working as closely as possible to the affected community. A staged response is called for, and this requires that state and local agencies establish a set of core competencies. The first competency is the ability to determine if a cancer cluster represents an excess cancer risk for the community. The second competency is the ability to respond to a cancer cluster concern. A third competency is the ability to link information about environmental contamination with cancer registry data. Most state health departments have developed protocols for responding to cancer clusters, however, these approaches and capacities vary from state to state.
High quality, population-based cancer registries are a critical tool for health departments to address cancer cluster concerns. CDC currently supports statewide, population-based cancer registries in 45 states, three territories, and the District of Columbia through the National Program of Cancer Registries (NPCR). The National Cancer Institute includes the remaining five states as part of its Surveillance, Epidemiology, and End-Results Program. These registries systematically collect and analyze cancer incidence and mortality data to identify and monitor cancer trends over time, guide cancer control activities, and suggest leads for further research. CDC's NPCR represents a unique opportunity to strengthen cancer reporting and registration in the United States. The NPCR collects information on cancer cases for 96 percent of the nation's population. Since 1997, the number of NPCR-supported state cancer registries that have been certified for quality by the North American Association of Central Cancer Registries has increased from nine to 29.
Data collected by state cancer registries can be used to guide planning and evaluation of cancer control programs; help set priorities for allocating health resources; and advance clinical, epidemiologic, and health services research. Cancer registry data is essential to be able to determine cancer patterns among various populations, to monitor cancer trends over time, and to identify and evaluate suspected clusters of cancer.
To maximize the benefits of state-based cancer registries, CDC is developing the NPCR-Cancer Surveillance System for receiving, assessing, enhancing, aggregating, and disseminating data from NPCR programs. This system will provide valuable feedback to help state registries improve the quality and usefulness of their data, and the system could support important data linkages with other cancer databases. Availability of data on a regional and national level will also facilitate studies in areas such as rare cancers, cancer among children, cancer among racial and ethnic minority populations, and occupation-related cancer.
Effective state health departments are reliant on experience staff who can access and use cancer registry information, interpret these data and act appropriately upon the results. CDC is currently exploring various strategies to meet these needs.
When we are able to identify environmental health hazards in affected communities and link cancer registry information with environmental exposure data, states well be able to better address community concerns.
The CDC and ATSDR Roles
CDC and ATSDR respond to cancer clusters by providing infrastructure support, national leadership, and technical assistance to states. Technical assistance has included peer review and consultation, field investigations, and assessment of environmental exposures. CDC has enhanced state infrastructure by funding state-wide population based cancer registries that enable health departments to review cancer incidence data and assess reported cancer clusters. In 1989, CDC sponsored the National Conference on the Clustering of Health Events; the proceedings appear in a supplement to the American Journal of Epidemiology (volume 132, July 1990). In addition, CDC published Guidelines for Investigating Clusters of Health Events in July 1990. The guidelines can be accessed at: http://www.cdc.gov/mmwr/preview/mmwrhtml/00001797.htm CDC continues to review these documents and the current science to be able to revise guidelines as appropriate.
ATSDR and CDC are involved in responding to cancer clusters. I have already mentioned CDC's support of state-wide cancer registration. CDC conducts exposure assessments and epidemiologic studies that evaluate how people are exposed to environmental hazards and that identify preventable environmental causes of cancer. CDC >s environmental health laboratory measures known and suspected cancer-causing agents in human blood and urine. CDC also addresses exposures to cancer causing-agents in the work place by conducting laboratory science and epidemiological investigations. CDC also responds to requests from employers, employees, and other government agencies for investigations involving possible work-related cancer.
ATSDR includes selected cancers among its seven priority health outcomes. ATSDR has responded to requests for cancer cluster investigations, especially those near hazardous waste sites. In addition, ATSDR educates concerned communities about cancer causes and prevention and publishes Toxicologic Profiles, a series of 137 monographs about cancerous and other health effects of hazardous substances, chemicals, and compounds found in waste sites. ATSDR also has been involved in research projects about the relationship between environmental exposure and the development of selected childhood cancers.
CDC and ATSDR are working toward a number of activities to assist state health departments respond to cancer cluster and other inquiries related to potential health risks from environmental exposures. CDC is establishing a single point of contact through which all of these disease cluster inquiries might flow. This office would coordinate the CDC and ATSDR response, drawing upon needed expertise throughout CDC and ATSDR and other Federal agencies. CDC, in coordination with state and local health departments will develop recommendations or guidelines for responding, identifying, and following-up on disease cluster inquiries.
We are in the process of developing a public health system that is capable of monitoring exposure to chemicals linking the monitoring data to actual health outcome information, and utilizing the results to identify and respond to disease cluster inquiries. This will require a partnership among CDC, ATSDR and state health departments. Disease cluster investigations have rarely led to new discoveries into the causes of cancer, developmental disabilities, and other health outcomes. However, other positive public health outcomes can result. One example comes from a community in California. At this site, a pesticide investigation did not find any causal links between environmental exposure and disease; however, it did lead to the implementation of many positive public health actions such as increased health insurance coverage, pesticide tracking and better working conditions.
CDC and ATSDR will continue to work with states on their disease registries and help provide public health professionals with the knowledge and skill to use these systems to respond to the public. CDC and ATSDR are working with the states to build their environmental public health capacity. Through comprehensive, coordinated efforts and in partnership with many governmental, nongovernmental and community-based organizations we will continue to improve America's environmental public health will be assured.
Thank you for the opportunity to testify before you today. I would be happy to answer any questions you might have.