Exposures And Conditions Of Acute Environmental Origin

Characteristics of Environmental Health Field Investigations

Field investigators face special challenges when confronted with exposures or disease clusters that might be related to contaminants or environmental factors. Challenges can include accurately assessing human exposure and determining a case definition and linking exposure to adverse health effects. Communication with potentially affected populations about risk and about actions to reduce risk is particularly challenging in environmental field investigations1.

The scope of this chapter is limited to the investigation of short-term exposures and resultant acute diseases or symptom clusters of environmental origin. Early, important examples of such investigations include the mass methylmercury poisoning of the population around Minamata Bay in Japan2 and exposure to dioxins after an industrial accident in Seveso, Italy3. In acute events, exposures are likely to be high and episodic, and the adverse health outcome might be detectable or measurable immediately or within days or weeks. Guidance documents for the public health investigation of clusters of disease of long latency are available for suspected clusters of cancer or birth defects but will not be discussed here45. Similar to these guidance documents, this chapter emphasizes a stepwise approach to investigation and transparent communication with potentially affected communities at all stages.

For this chapter, the "environment" includes contaminants that could cause an adverse health outcome in air, water, soil, food, or consumer products. Exposure factors can be physical (e.g., radiation or extreme weather) biological, or chemical. Chemical factors can be synthetic (e.g., organophosphates) or naturally occurring (e.g., arsenic and biological toxins).

The trigger for an environmental field investigation might be the unusually increased occurrence of acute symptoms or characteristic set of symptoms (syndromes) in a population, which is suspected to be causally related to some environmental factor. Community members, alert clinicians, or a disease surveillance system might bring these symptoms to the attention of health investigators. Syndromic surveillance systems can be particularly useful and are commonly used to detect syndrome increases for public health action. The data sources for syndromic surveillance vary by jurisdiction but might include monitoring data from hospital emergency departments, poison control centers, over-the-counter drug sales records, or other sources6. The field investigator will have the following objectives, which are in common with most epidemiologic investigations:

• Developing a working case definition.
• Identifying who has become ill.
• Defining the disease or symptom cluster in space and time.
• Identifying the likely causal agent of the adverse health outcomes.
• Recommending or taking actions to prevent further exposure and prevent additional cases of disease.
• Considering conducting an environmental assessment, where appropriate.

However, the trigger for an environmental field investigation also might be exposure or suspicion of exposure to an environmental agent, rather than knowledge that a cluster of symptoms or disease already has occurred. Exposure itself might be sufficient grounds to initiate immediate public health interventions, for example, when a release of a highly toxic chemical has occurred. Like disease clusters, exposures also might come to the attention of health investigators from community members or alert clinicians or through partners (e.g., environmental protection agencies or poison information centers), environmental monitoring systems, or emergency response personnel. In these circumstances, the field investigator might have one or more of the following objectives:

• Identifying the likely environmental causes of the adverse health outcomes.
• Confirming and (if possible) quantifying the magnitude of exposure and route of exposure, taking into account processes that may have changed the intensity of exposure such as dispersion or dilution.
• Defining the potentially exposed population.
• Determining whether exposure is sufficient to result in adverse health effects (includes assessment of inherent toxicity of the exposure, suspected dose, and pathway and duration of exposure).
• Determining whether exposure has in fact resulted in symptoms or disease in the exposed population, if sufficient time has elapsed for occurrence.
• Recommending or taking actions to prevent further exposure and prevent additional cases of disease.

Environmental health investigations usually require assembly of multidisciplinary teams whose makeup will depend on the exposure and health concern. Understanding exposure might require expertise in chemistry and the environmental or biological fate of the contaminant, and likely transport of contaminants in various environmental media (air, water, or soil), or methods of exposure measurement or modeling. Understanding the potential for health impacts requires expertise in toxicology, epidemiology, and environmental or occupational medicine.

Investigation teams also need staff trained in risk communication and community or media relations to gather and disseminate health information during and after acute exposure events. These skills are especially important because environmental health field investigations often are conducted while communities experience fear, uncertainty, mistrust, and anger, and during intense media attention.

Environmental health field investigations should follow a stepwise approach. Some steps should be performed simultaneously because of the acute nature of some situations; some investigations might not entail all steps.

Collecting Preliminary Exposure and Disease Information

Regardless of the initial trigger, capture as much information as possible from the initial alerting source (community member, clinician, the media, emergency responders, or surveillance and monitoring systems). Gather information from several corroborating sources, including reports of responses to previous, similar events, for more reliable situational awareness. The sources will be dictated by the specific circumstances but might include local, state, and federal environmental regulatory authorities, health agency surveillance programs, emergency response on-scene coordinators, hazardous materials units, local hospital emergency departments, and poison control centers. Early in the response, keep an open mind about the possible nature, magnitude, and source of exposure. Exposures can occur from an unexpected source, such as a misapplied pesticide or imported product.

When reports of symptoms or disease are the trigger, gather information about the number and ages (and other relevant demographic factors) of persons reporting disease or symptoms, dates and times of symptom onset or disease diagnosis, the nature and severity of illnesses, whether ill persons have sought medical attention or care, and locations or settings where persons became ill. Gather duration of symptoms and timing of onset for each symptom because this progression could be a key to contaminant identity.

Initial exposure information might include eyewitness reports of visible plumes of gases or particulates, accounts of unusual odors or tastes, and discoloration of soils or water. Emergency responders might have collected data using portable air monitors indicating nonspecific contamination of air or gathered samples from surfaces or other contaminated media. Such information can be useful to reconstruct exposure patterns retrospectively. As early as possible during the investigation, document specific measurements of chemical contaminants in environmental media.

Initial impressions of the magnitude of an event might be based on incomplete information and appear minimal; further investigation, including review of all relevant surveillance and monitoring data, might reveal a wider impact. As early as possible, consider protective interventions and mitigation actions, even when information about exposure and illness is preliminary. Early mitigation to contain exposure can be important given that some environmental exposures have delayed effects, concern might exist about additional exposures, or the population at risk has not yet been fully described (e.g., with potential product tampering or contamination). Examples of mitigation actions include elimination of a point source, evacuation, sheltering in place, and engineering controls. Appropriate interventions also can build or maintain public confidence and trust.

Developing a Risk Communication Plan

In the age of widespread use of social media, frequent class action litigation, and sensationalized movie portrayals of environmental contaminant impacts, there is renewed emphasis on effective public health risk communication on environmental issues. In any field investigation, developing and implementing a risk communication strategy as early as possible is essential, emphasizing transparency, good listening skills, and assurance that public health investigators are actively looking into an issue9. The risk communication plan is critical to build trust and support that investigation findings will be credible and accepted by affected communities. Situations that trigger formation of an incident management structure will require coordination of communication with a joint information center. An effective risk communication approach during an environmental investigation will adhere to the following principles10:

• Accept and involve the public as a legitimate partner. Community members may have critical insights about local environmental exposure issues.
• Listen to the community's specific concerns. Find out what people are thinking and what they want to know.
• Be honest, frank, and open. As soon as possible, disclose what is and is not yet known about environmental risks.
• Coordinate and collaborate with other credible sources. Involve independent communication partners (e.g., community physician) whom the community might already trust.
• Meet the needs of the media. Be accessible to reporters and prepared with concise messages.
• Speak clearly and with compassion. Avoid technical jargon, acknowledge and respond to emotions expressed, and emphasize actions under way to reduce risk.

As part of risk communication planning and preparation, develop specific objectives for particular stakeholder audiences. Whenever possible, be prepared with pretested risk messages that are adaptable to emergent situations.

Fear and outrage are magnified when exposure to contaminants is imposed and outside of individual control and when a community's expectation of safe air, water, food, or consumer products is violated. Stressful events reduce the ability of community members to process and assimilate information, so state the most important public health messages first and repeat them frequently.

Assembling a Multidisciplinary Investigation Team

To the degree possible, assemble an internal team with skills in epidemiology and environmental exposure assessment that address the specific situation. From the outset, include a risk communication or media relations specialist on the team. Team members also could include representatives of local or state health and environmental agencies and emergency response units. Try to establish partnerships with, and obtain assistance from, federal health and environmental resources.

As early in the investigation as possible, assemble independent or outside subject matter experts whose assistance might be needed. This team could include environmental and laboratory-based scientists, industrial hygienists, physicians or other clinicians trained in occupational or environmental medicine, toxicologists, and poison control directors. Some incidents may require coordination with law enforcement.

Developing Case Definitions and Confirming Diagnoses

Use preliminary information about the nature of symptoms and illnesses to establish a working case definition for further analysis of the situation. The case definition can be tightened, expanded, or otherwise modified as information emerges, but it should include symptoms or sets of symptoms, the period of onset, and geographically relevant information. If an environmental exposure is known or suspected, the case definition should take into account what is known about the toxic effects or biological responses after exposure, taking latency, exposure pathway, and suspected dose into consideration.

Interview each person whose illness meets a working case definition. In an investigation driven by exposure information, consider interviewing persons with suspected exposure to gather information about symptoms or illnesses, including those possibly related to the exposure of concern. To facilitate data collection, develop or refine a case interview and abstraction form that addresses demographics, symptoms, symptom onset, risk factors, possible exposures, and medical system encounters in relation to time and place. When useful as part of a case definition, consider collecting and analyzing biological specimens for appropriate measures.

When considering the collection and use of health records, know the jurisdictional authority for collecting and inspecting these records and any limits placed on this authority by law or regulation. This understanding is particularly important in regard to conditions not specifically reportable in the state. Many states require reporting of specific noninfectious diseases to public health authorities. Additionally, most states have laws and regulations that require reporting of unusual clustering of disease or unusual health events to public health authorities.

Characterizing Exposure: Who Has Been Exposed and to How Much

Regardless of whether an apparent increase in disease or an exposure event triggers an investigation, accurate assessment and quantification of the population's exposure to an environmental agent is critical. However, exposure assessment can be difficult or impossible in many circumstances. For example, chemical releases during disaster incidents can occur quickly and disperse before sampling or monitoring equipment can be brought to the scene. In some situations, no scientifically reliable or validated environmental or biological monitoring measure (for example, of a chemical in air, water, blood, or urine) may be available, making characterization of the exposure even more difficult.

When applicable, case definitions should include clinical measurements of human exposure, particularly for situations involving exposure to chemicals with relatively clear relationships between exposure level and clinical outcome, such as for certain pesticides, metals (lead, mercury), or carbon monoxide1718. For example:

• Exposure to organophosphate pesticides can be defined on the basis of changes in cholinesterase values.
• Evidence of unusual mercury exposure might include a clinical measurement of urine mercury.
• Carbon monoxide poisoning definition might include assessment of the carboxyhemoglobin value.

Biomonitoring or chemical measurements in people can also help determine that exposure has not resulted in widespread contamination1920. Biological measurements of chemicals or metabolites must be understood in the context of the chemical's pharma-cokinetics, which dictates the timing of specimen collection and the biological medium to be sampled (for example, blood, urine, exhaled breath, or hair). For chemicals with short half-lives, specimens might need to be collected and measurements made within hours of exposure to be interpretable as an exposure metric. For some chemicals, clinical laboratory measurements might not be relevant because an analytical method is unavailable or testing could not be done in a time period relevant to the assessment of exposure.

The National Center for Environmental Health of the Centers for Disease Control and Prevention has established national reference values for many environmental chemicals21. These values can be used as cutoff concentrations in a case definition or as comparison for population exposure results in community surveys that use biological monitoring.

Completing Case Ascertainment

Once a case definition is established, attempt to ascertain all possible cases by using all relevant sources of data. These data sources might include syndromic surveillance systems, other potentially relevant surveillance data systems that collect laboratory findings, emergency department medical records and poison control center information (See Outbreak of Pesticide Poisoning from Contaminated Watermelons), inpatient hospitalization records, and self-reports or interview responses. When most of the instances of exposure have occurred at an event or exposure is widely dispersed (such as product contamination or chemical release in a public place), locating potentially exposed persons might require other methods. Use of conventional print and broadcast media, social media, blasts to providers and facilities, email listings, and other methods might help capture as many cases as possible.

Characterizing the Disease Cluster

Summarize case information, paying attention to basic demographics, place, and time. Constructing and examining the classic epidemiologic curve (the histogram of the number of new-onset cases by date or time) is just as useful in environmental investigations as in field investigations of infectious sources (See Acute Selenium Toxicity with Dietary Supplement). The epidemiologic curve can be considered in conjunction with such events as dates of product use, chemical release, and probable exposure, and with knowledge of the lag time between exposure and measured health effect (that is, latency).

Dates, times, and circumstances of symptom resolution can also be important. For example, affected persons might report symptom exacerbation when they are in specific locations, possibly pointing to locations or exposures of specific concern. Symptom abatement when absent from a location (work or school) also is an important detail.

Mapping the locations of cases during symptom onset can yield important clues and suggest hypotheses about exposure and symptoms or disease and actions to be undertaken to prevent disease.

Developing Preliminary Hypotheses and Analyzing Health and Exposure Data

On the basis of data collected, investigators should develop preliminary hypotheses about the relationship between the exposure and symptoms, taking into consideration the following questions:

• Are the symptoms or illnesses that define the cases biologically plausible on the basis of what is known or suspected about the nature and magnitude of exposure?
• Were symptom onset times congruent with the timing of exposure and what is known about the latency of effect?
• Does the epidemiologic curve suggest a discrete event, multiple episodes of exposure, or continuous exposure?
• Does a map of the locations of cases (at time of exposure or disease onset) suggest something about the nature of the source (e.g., localized or widespread, through air or water)?

At this point, ask whether the illness or disease cluster could be associated with an exposure or multiple exposures. Comprehensive resources on toxicologic effects of chemicals are readily available for consultation on exposure–symptom relationships26272829.

Depending on how the hypothesis is framed, consider testing differences in the proportion of persons with symptoms or disease by varying levels of measured or estimated exposure. The exposure measure to be tested might be physical proximity to a suspected exposure source, environmental measures or modeled values, or biological metrics. Also, ask whether mean levels of exposure differ by varying severity of specific health outcomes. Consult textbooks on standard statistical methods (e.g.,30).

Preliminary analyses might point to the need for more sophisticated methods to better understand the data gathered. Similarly, a systematic epidemiologic investigation might be needed to link exposure and illness in at-risk populations, although this link might be difficult to confirm. In this stage of the investigation, engaging subject matter experts is especially relevant.

Determining the Need for Further Systematic Study

The primary goal of any public health investigation is to prevent further disease or death. In an environmental investigation, mitigation efforts might achieve this goal without benefit of detailed environmental or biological information. However, a public health agency can consider a number of next steps, particularly when working with subject matter experts, to refine the investigation. These steps can include exposure modeling (such as air dispersion modeling) to refine exposure estimates. Other classic next steps include a case– control study, a retrospective cohort study, or other relevant study design. Sometimes more extensive use of existing information, including vital statistics, registry data, or hospitalization data, can provide appropriate information. Use of cluster detection methods to refine spatial and temporal bounds of a cluster or to locate other possible clustering of disease also is possible. Most of these next steps are resource intensive and might not lead to confirmation of the association between exposure and cases. Consider the resources available to public health, community needs, and expectations and scientific soundness of any approach.

Summarizing Findings and Developing Conclusions and Recommendations

Communicate about the status of the investigation to the community and other stakeholders as work proceeds, and prepare a written summary report of methods and findings at investigation end. In the final report, include clearly articulated conclusions that are supported directly by the findings and recommendations to the community and other stakeholders.

Present the summary investigation report to the community and other stakeholders in settings, places, and times convenient for the community. Tailor findings and prevention messages to different audiences, taking into account literacy level and language barriers that might impact the effectiveness of written and spoken communication.

Implementing Prevention and Control Measures to Reduce Exposure and Illness

Consider prevention and control interventions throughout each step of the investigation. These interventions will usually involve work with environmental regulatory and emergency response partners to take actions to prevent further human exposure. In emergent situations, especially early on, interventions will have to be undertaken in the face of substantial uncertainty. For example, steps should be taken immediately to stop exposure to an elemental mercury spill or release in a residential or school setting. Evacuation of building occupants might need to be considered as soon as possible, followed by appropriate site cleanup steps (See Carbon Monoxide Poisoning at an Indoor Ice Rink).

Other examples of public health actions that can mitigate exposure include

• Providing bottled water to private well water owners after discovery of high levels of contamination.
• Public messaging on prevention of carbon monoxide poisoning before, during, and after power outages related to storms or other disasters.
• Warnings or recalls related to contaminated consumer or food products.

Sometimes an investigation calls attention to the need for larger, more proactive primary prevention efforts that are not necessarily community-specific, such as new legislation (e.g., requiring carbon monoxide detectors in new residences or rental properties), increasing training (e.g., tailored training for emergency response personnel on chemical release), setting new standards (e.g., establishing buffer areas for facilities that handle flammable or toxic chemicals in large quantities), or increased outreach and education (e.g., providing brochures for private well owners on proper well maintenance and testing). Similarly, investigators should take the time to consider lessons learned from the incident response and make recommendations regarding agency best practices for improving the effectiveness of responses to future events.

Field investigations of exposures and diseases of environmental origin require unique partnerships and expertise that might be outside of traditional public health. Effective risk communication is a critical component of response in an environmental investigation. Public expectations of clean food, water, and living areas place increased expectations on public health during these investigations. Public health needs to maintain expertise in environmental issues, maintain strong partnerships with state and federal environmental partners and be skilled at risk communication to successfully complete environmental investigations.