At the turn of the 20th century, the American population faced significant health challenges. The recent shift in population from rural to urban that accompanied industrialization resulted in overcrowding in dilapidated housing served by inadequate water supplies and nonexistent waste disposal systems. These conditions led to continued outbreaks of infectious diseases that ravaged the population. In 1900 one-third of all deaths were caused by pneumonia, tuberculosis, or diarrhea, and 40% of these deaths were among children younger than 5 years (Bureau of the Census 1906). After the discovery of the “germ theory” of disease, much of the dramatic decrease in mortality from infectious disease in Western civilization was attributable to environmental public health measures such as disinfection of water, food safety regulations, and housing improvements, among others [Centers for Disease Control and Prevention (CDC) 1999].

The last half century witnessed a dramatic shift in the health burden of the U.S. population from infectious diseases to diseases such as cancer, birth defects, and asthma, many of which may be associated with environmental exposures. During the same period, advances in industrial science and technology led to the development and production of tens of thousands of chemical compounds. Unheard of 50 years ago, these chemicals are now ubiquitous in our air, water, food, workplaces, and homes. Mankind has benefited substantially from these products, but the health implications of long-term exposure to low levels of these compounds are not well understood. The American people feel strongly that the environment plays a role in their health. A poll taken in 1999 by the Pew Charitable Trusts found that 87% of Americans believed that environmental factors such as pollution cause increased rates of diseases and health problems (Pew Charitable Trusts 1999).

In September 2000, after 18 months of review, the Pew Environmental Health Commission released a report on the state of environmental public health in the United States (Environmental Health Tracking Project Team 2000). The commission found that the environmental public health system was fragmented, neglected, and ineffective. The report stated that the current system does not have the capability to respond adequately to environmental threats. The first of a number of recommendations made by the commission called on the federal government to establish a national environmental public health tracking (EPHT) network to link information on environmentally related diseases, human exposures, and environmental hazards. The information from this tracking network would be used to respond to, and eventually reduce, the burden of these diseases on the nation’s population. The commission estimated the cost of this tracking network to be $275 million annually.

Public health surveillance or tracking systems are critical in preventing and controlling disease in populations. Accurate and timely surveillance data permit public health authorities to determine disease impacts and trends, recognize clusters and outbreaks, identify populations and geographic areas most affected, and assess the effectiveness of public health interventions (Teutsch 2000). Most of the public health surveillance currently in place in the United States focuses on infectious diseases. We urgently need a more comprehensive national approach to the collection and analysis of noninfectious disease data and the integration of that information with environmental hazard monitoring and exposure data. The availability of these types of data in a standardized tracking network will enable researchers and health authorities to begin to understand the possible associations between the environment and adverse health effects.

Environmental public health tracking is the ongoing collection, integration, analysis, and dissemination of data from environmental hazard monitoring, human exposure tracking, and health effect surveillance (Figure 1). Currently, the Centers for Disease Control and Prevention (CDC) is leading an initiative to build a national EPHT network that will meld data from these three components into a network of standardized electronic data systems and will provide valid scientific information on environmental exposures and adverse health conditions and the possible spatial and temporal relations between them.

CDC and our partners are applying the conceptual model first proposed by Thacker et al. (1996) to design the EPHT network. This model outlines the causal pathway starting with a hazardous agent present in the environment, followed by a population exposed to this agent and receiving a dose, and ending with a clinically apparent adverse health effect. Hazard, exposure, and health effects tracking represent data collection points along this continuum. Collecting, analyzing, and disseminating data from any one of these types of data systems or a combination of them provide important information for public health practice and comprise environmental public health surveillance activities. Development of a national EPHT network depends on the availability, quality, timeliness, compatibility, and utility of existing hazard, exposure, and health effect data. Both Thacker et al. (1996) and the Pew Commission (Environmental Health Tracking Project Team 2000) describe data that could potentially comprise part of a national EPHT network, such as vital statistics and the Aeromatic Information Retrieval System. Improvements to existing data systems, development of new systems, and integration of the data from these systems will be required to fully implement this network.

Hazards include chemical agents, physical agents, biomechanical stressors, and biologic toxins that can be found in our air, water, soil, food, and other environmental media. Often, data regarding these hazards are collected for regulatory purposes, and the characteristics of data collected are mandated by federal or state statutes. Thus, the types of data collected, the frequency of data collection, the location of data collection, and the collection methods may be optimal for enforcement activities but are less than ideal for public health surveillance use. For example, the U.S. Environmental Protection Agency’s (EPA) Safe Drinking Water Information System/federal version (SDWIS/FED) collects data from states on drinking water utilities’ noncompliance with federal drinking water standards (U.S. EPA 2004b). These data allow the U.S. EPA to track contaminant levels and to determine whether new regulations are needed to protect human health. However, the utility of SDWIS/FED for environmental public health surveillance is limited because actual monitoring data are available at the federal level only when results exceed the maximum contaminant levels, and the consistency of data elements over space and time can vary (Niskar 2003). At a minimum, hazard data included in the national EPHT network will need to be obtained through routine standardized data collecting and reporting and must have ongoing quality control, appropriate geographic coverage for the population at risk, and be available in a timely manner.

Exposure tracking is the monitoring of individuals, communities, or population groups for the presence of an environmental agent or its metabolite. Exposure data can include estimates derived from hazard data through sophisticated modeling. For example, the U.S. EPA and the National Oceanic and Atmospheric Administration are leading a project to model source emissions data, air monitoring data, and meteorologic data to forecast population exposure to ozone (U.S. EPA 2004c). Another example is the work conducted by the National Cancer Institute to estimate county-level exposures and thyroid doses received by American citizens from iodine-131 in atmospheric nuclear weapons testing fallout (National Cancer Institute 1997). Exposure data can also include direct measurements of individual exposure obtained from use of personal monitors such as passive air samplers and personal radiation dosimeters. However, neither of these types of exposure data is currently available for tracking exposures in an ongoing, systematic manner.

Exposure tracking of biomonitoring data represents the only method that actually measures the presence of hazardous agents in the human body. This type of exposure data provides information on the levels of chemicals or their metabolites in human biologic specimens such as blood or urine. Depending on the chemical agent, these measurements can serve as indicators of recent, long-past, or cumulative exposure to a hazard. For example, chemicals such as benzene are metabolized and excreted rapidly from the body, whereas the lipophilic compounds tetrachlorodibenzo-p-dioxin and polychlorinated biphenyl are retained for years (Thornton et al. 2002). Although more research is needed to understand fully the complex relationship between external hazard concentrations, internal dose, and health effects, biomonitoring data are an important component for comprehensive environmental public health surveillance.

Currently, few biomonitoring data are being tracked. At the national level, human samples are collected through the National Health and Nutrition Examination Survey and analyzed and reported by CDC in the “National Report on Human Exposures to Environmental Chemicals.” Blood and urine levels of 116 environmental chemicals are currently available for a sample of the noninstitutionalized U.S. population (CDC 2003). At the state level, state laboratories have limited capacity for biomonitoring. Childhood blood lead levels are the only measures that are routinely collected across most states, and these levels are collected in screening programs of high-risk children.

The final component in the conceptual model of Thacker et al. (1996) is health effects tracking, which represents traditional public health surveillance efforts. Disease registries, vital statistics data, annual health surveys such as the National Health Interview Survey, and administrative data systems such as hospital discharge data are sources that have been used for tracking health conditions. These varied sources have created a patchwork of health effect measures, and reliance on these data demonstrates the need for standardization for most disease surveillance. EPHT limits itself to those health effects with scientific evidence of possible environmental etiology. Health end points recommended as starting points for a national EPHT network by the Pew Commission focus on the following chronic conditions: birth defects; developmental disabilities such as cerebral palsy, autism, and mental retardation; asthma and other chronic respiratory diseases such as bronchitis and emphysema; cancer; and neurologic diseases, including Parkinson disease, multiple sclerosis, and Alzheimer disease. Additionally, the commission recommended tracking sentinels of exposures and health outcomes requiring rapid public health responses such as heavy metal poisoning and pesticide poisoning (Environmental Health Tracking Project Team 2000).

A key distinction between EPHT and traditional surveillance is the emphasis on data integration across health, human exposure, and hazard information systems (Figure 1). Our program to build a national EPHT network is the first national effort to provide the United States with standardized data from multiple health, exposure, and hazard information systems, that includes linkage of these data as part of regular surveillance activities. The network builds on separate ongoing efforts within the public health and environmental sectors to improve health surveillance, hazard monitoring, and response capacity (CDC 2004; U.S. EPA 2004a). This system will be used to identify potential relations between exposure and health conditions that either indicate the need for additional research or require intervention to prevent disease, disability, and injury.

A neglected public health infrastructure and the lack of a trained workforce are monumental challenges to establishing a national EPHT network. In 1988 the Institute of Medicine (IOM) referred to the American public health system as a “shattered vision” (IOM 1988). Fifteen years later, a follow-up IOM committee found that improvements in the public health infrastructure and workforce development were still needed to ensure provision of essential public health services and to address emerging public health issues (IOM 2003). A trained, motivated, and dedicated workforce will be a necessity not only for the establishment of a national EPHT network but also for ensuring the health of the American people through the coming decades.

Depending on resource availability, the national EPHT network may need to build some surveillance infrastructure from the ground up. Surveillance systems currently do not exist at the local, state, or national levels to track many of the exposures and health effects that may be associated with environmental hazards (CDC 1998, 2000). Kass et al. (2004) describe the challenges of pulling together pesticide data for environmental public health surveillance. When information systems do exist, quality of the data, data vocabularies, and case definitions vary, and electronic reporting is still not an option for all sources of data (Goldman et al. 1992; Steenland and Savitz 1997). Laflamme and VanDerslice (2004) discuss the lack of standard environmental health questions in the Behavioral Risk Factor Surveillance System. Mather et al. (2004) present a table describing uses and limitations of hazard, exposure, and health effects data. These limitations present significant challenges to developing a national integrated data network. Standardization of technology and data specifications is ongoing within CDC (CDC 2004) and the national EPHT network is part of this effort. CDC and its partners are currently identifying data needs of their constituents and evaluating mechanisms and costs for improving data and filling data gaps.

The national EPHT network has received attention from the media, elected officials, and the public. Along with that attention has come some misunderstanding of the capacity of the network to provide answers to etiologic questions. As a surveillance system, EPHT cannot answer questions about causes of diseases. It can, however, generate hypotheses about etiology and identify areas where additional research is needed. We expect the national EPHT network will provide information to estimate the magnitude of a health effect in the population at risk, to detect epidemics or clusters, to document the distribution and spread of a health effect, to evaluate interventions, and to facilitate planning (Teutsch 2000).

Being able to link health, exposure, and hazard data on an ongoing basis will enable environmental public health practitioners to evaluate the spatial and temporal relations between environmental factors and health. However, detecting even these ecologic relations through the network will require careful analysis and interpretation. The pitfalls of drawing etiologic conclusions based on these ecologic relations are well documented and include issues such as confounding, measurement error, variation in event classification, and migration patterns (English 1996; Greenland 2004). In this mini-monograph, Mather et al. (2004) provide further discussion on ecologic bias in describing the statistical framework for analyzing the exposure, hazard, and disease relationship.

One factor to consider in interpreting relationships seen from analysis and visualization of tracking data is the lag time for most health effects thought to be associated with exposure to environmental hazards. Disease may occur in a specific area during a prescribed time, but exposure associated with the disease may have occurred months, years, or even decades earlier. Other factors contribute to the difficulties in characterizing environmental exposures because of the uncertainties inherent in exposure modeling and the mobility of the American public, whether related to daily commutes or relocating residence. Finally, many of the health effects of interest for environmental public health have multi-causal pathways. Other factors will confound or modify our ability to interpret the role of specific environmental exposures on disease risk when analyzing surveillance data.

EPHT is the ongoing collection, integration, analysis, and dissemination of environmental hazard, exposure, and health data. CDC and our partners are developing this approach for the EPHT network based on concepts from infectious and chronic disease surveillance and environmental hazard monitoring. The unique feature of the national EPHT network is the emphasis on data integration and standardization from all sources to improve data utility to the end user. With adequate funds, the EPHT network will provide valid scientific information on environmental exposures and adverse health effects that will bridge the existing data gap and provide a foundation for actions to improve community health. A key component of the EPHT network is dissemination. This mini-monograph is an opportunity to disseminate the first lessons learned about the innovative process of developing a national EPHT network. The articles represent the diversity of partners, priorities, and activities that are underway to build the EPHT network and to provide more information to the American people on how the environment contributes to human health.