|Assessing the Health Consequences of Major Chemical Incidents - Epidemiological Approaches, 1992 (WHO - OMS, 1992, 104 p.)|
|1. Role of epidemiology in assessing health effects following a major chemical incident|
The three chronological stages of the evaluation and management of a chemical accident are called the planning and preparedness phase, the response phase and the follow-up phase.
Planning and preparedness
The preparedness phase takes place during the period before a chemical release. In practice, it is a continuous activity, with periodic updates and revisions. This is the time to prepare an efficient and effective system for emergency response (incident management), rehabilitation and follow-up. Activities in this phase include:
1. establishing and maintaining an inventory of potential risk sources, such as hazardous installations and transport routes;
2. establishing a chain of command and a network of cooperating emergency response services and expert consultants;
3. drafting emergency response guidelines and medical treatment protocols;
4. running collaborative (interagency) training sessions with every party involved in the emergency response;
5. obtaining all necessary equipment and supplies, or making arrangements to obtain them at short notice in case of an emergency; and
6. planning for an emergency under existing legislation with industry and local authorities.
Role of epidemiology
During this phase, an efficient and effective system should be prepared for initiating an emergency response and planning rehabilitation and follow-up. Adequate resources should be dedicated to this task. In this period the decisions can be made by consensus. Any activity that can be performed in the response stage should be included in the contingency plans developed in the preparedness phase.
Important stimuli for adjustment of the contingency plans in this phase are the experiences from previous emergency responses and/or training sessions. Specific activities include:
1. identifying the epidemiologists role in the planning team;
2. identifying population and health data sources;
3. identifying existing environmental monitoring networks;
4. identifying poison centres active in the area;
5. preparing for the planning and conduct of epidemiological studies;
6. specifying and preparing methods for rapid assessment of potential health effects, including facilities for collection, storage and analysis of biological samples; and
7. testing the methods for investigating disease outbreaks and performing other small surveys of acute incidents.
The response phase starts when it is recognized that an incident has occurred, and lasts as long as rapid interventions are conducted. As quickly as possible and under pressure of time, decisions are made according to the prearranged chain of command, and emergency response personnel attempt to comply with prepared contingency plans.
Activities in this phase include:
1. verifying the incident, and identifying the source and nature of chemical(s) and/or the nature of immediate health consequences;
2. terminating the incident and/or the associated chemical release;
3. preventing exposure to employees, emergency response personnel and the general population;
4. assessing the exposure and health outcomes;
5. assessing health risk to exposed individuals and to the population;
6. preventing and/or mitigating adverse health effects due to exposure, by advising the public and the authorities;
7. providing medical treatment of casualties; and
8. identifying the casualties.
Role of epidemiology
During the response phase, the epidemiologist undertakes health risk assessment, defines the populations at risk of different types of exposure, rapidly collects valid data on health status and exposures, and relates exposure data to information on health status. The epidemiologist should also be involved in evaluating the impact of the incident and, in this way, provide the background for the advice on preventive intervention measures given to the public and public health officials.
Carrying out epidemiological functions during the response phase is often difficult, because many emergency response personnel do not perceive the relevance of field epidemiology at that time. All public health professionals and emergency personnel must therefore understand the role of epidemiology and the need for data collection during the acute crisis. Epidemiological input in the planning and preparedness phase is essential to achieve this.
Several illustrations of epidemiological activities in the response phase of health assessments exist. For example, during the 1986 incident in Basle (see Annex), epidemiologists analysed daily mortality, inpatient and outpatient attendance and symptoms in different population groups (6). In the Shetland oil spillage in 1993, epidemiologists determined the immediate effects and collected baseline health data and biological measurements (7). The Annex provides some details of these incidents and describes the involvement of epidemiologists in their evaluation.
The follow-up phase encompasses the time after the termination of the rapid response activities. It lasts as long as effects of the incident can be expected to occur.
Once the acute phase is over, the general public tends to return to its usual activities, and becomes less interested in the incident or its consequences. In contrast, the people affected by the incident start the process of coping with the consequences. While more time is usually available to make decisions than in the response phase, public and political pressure may place time constraints on studies of health consequences.
Activities in this phase include:
1. rehabilitation, that is, restoring the affected area, its occupants, workforce and emergency response system to a state equivalent to or better than the original;
2. follow-up of exposed employees, emergency response personnel and the general population, including:
· the provision of medical, social, economic and psychological care;
· epidemiological follow-up of the incident;
3. risk assessment of the health consequences of the incident;
4. follow-up and/or clean-up on the environmental consequences of the incident, which (from a public health perspective) may cause secondary exposure through, for example, contamination of the food chain and/or drinking-water; and
5. appraisal of the emergency response phase.
Evaluation of an incident should lead to recommendations to prevent repetition and to adjust emergency response plans where they did not perform perfectly.
Role of epidemiology
In the follow-up phase, health risk assessment should be continued whenever there are reasons to suspect medium- or long-term effects. Such effects may include disturbances of lung function, neurological and behavioural disorders, allergy, adverse pregnancy outcome and cancer. A decision as to whether such adverse effects may be expected must be made promptly, with the collection of baseline data on both exposure and earlier health status commencing as soon as possible. Urgent toxicological expert consultations are usually necessary and should be carried out without delay, for example, by contacting poison information centres. Advice from an occupational health specialist may also be valuable.
Epidemiological follow-up should include the activities listed in Box 3. They may be undertaken:
· to respond to public concern and to alleviate the worries of people exposed in the incident and those living in the vicinity of chemical plants;
· for the purposes of current or future litigation or compensation;
· owing to political pressure to do something;
· to expand knowledge on health effects in exposed populations; or
· to develop evidence of a causal connection between exposures and health effects.
A considerable part of the information needed in the follow-up phase must be collected during the response phase. This should be anticipated during the planning and preparedness phase. Further, in the longer-term aftermath of an incident, official and public interest is likely to wane. It is therefore important for public health authorities at all levels to accept the need to support and fund follow-up studies, and to build this consideration into the planning and preparedness phase.
Box 3. Epidemiological activities in the follow-up phase
These activities include:
· following up cases or the exposed population;
Follow-up studies should be carefully designed and implemented in order to overcome particular problems. These problems are related to:
- size (and its effect on study statistical power); and
- mobility and cooperation (maintaining high response rate during follow-up);
· health outcomes:
- the unknown (but often long) latent period from exposure to effect;
- the changing background morbidity of the population over a long time;
- the need to separate the effects of exposures in multifactorial diseases;
- the availability of valid and comprehensive data; and
- possible bias in subjective assessment of health status related to special interests (such as political issues or the prospect of financial compensation);
· availability of reliable quantitative data on exposure;
· technical and feasibility issues:
- focus on long-term studies during the acute phase;
- the need for resources to obtain and store samples and to set up registers in acute situations; and
- the lack of standard definitions, and of measurement tools to use and to permit comparison of studies.
Properly implemented follow-up studies provide unique opportunities to obtain information on the long-term results of exposure to chemical substances. Thus, they should be seriously considered as part of the response to all chemical incidents.