Epidemiology
WORKING GROUP III
The initial purpose and goal of epidemiologic research would be to establish the magnitude of the problem caused by the MCS phenomenon in the population and to characterize the cases sufficiently for further work. Full use of epidemiologic methods to study this issue is handicapped by the lack of a precise, agreed upon case definition. The lack of understanding of mechanisms and of the exposure patterns involved also restrict epidemiologic approaches at this time.
An important distinguishing feature of the syndrome is that the concentrations of contaminants to which the individual responds is reported to be orders of magnitude below the concentration to which the majority of people respond. Because the lack of an agreed upon case definition is a limiting factor in making progress, studies aimed at improving this definition should receive emphasis.
An early priority should be a multi-center clinical case-comparison study in occupational/environmental medicine clinics and other appropriate facilities. Patients who report responding with signs and symptoms to concentrations of environmental chemicals orders of magnitude below where the normal public responds world be enrolled. The study would take place at multiple sites using an agreed upon set of criteria. Clinical histories, batteries of tests and structured interviews should be used to define case characteristics and natural histories. The efficacy, specificity and sensitivity of different tests and instruments should be evaluated and validated between centers. The tests should, among others, assess psychologic-psychiatric conditions, immune function, neurotoxic reactions, etc. The study subjects would be compared with clinic controls (e.g., low back injuries) for the purpose of understanding case definition, the descriptive epidemiology of cases and general cross-sectional study.
The information from the multi-center study can then be used to construct a population-based study to determine the prevalence of the MCS entity and associated conditions. The provisional nature of the case definition suggests that it would be important for a broad set of symptom prevalences to be determined to allow flexible construction of a variety of definitions. Such descriptive studies could be started with review of the Health Interview and NHANES surveys conducted by the National Center for Health Statistics. It is possible that one or more of the population-based cohorts such as the Framingham,
Alameda County, Tecumseh, or Washington County cohorts could have an addition to follow-up surveys to probe for prevalence of conditions such as MCS.
Population based methods should also be used to determine the basic descriptive epidemiology of certain multi-organ conditions linked by some to MCS, such as SLE, scleroderma, MS and somatization disorder.
Epidemiology has an important role to play in supporting methods evaluation and development for test instruments used in clinical studies as well. Determination of normal ranges for new test modalities, establishing the sensitivity and specificity of screens and biomarkers, and the construction of survey instruments are examples where epidemiologic input is important and we recommend the inclusion of such expertise in these areas. The committee felt that the follow-up of a defined population subjected to a discrete and sudden chemical exposure (such as a spill or pesticide misapplication) would also be useful to assess the initiation of hypersensitivity to environmental chemicals and its natural history. It recommends that a protocol for evaluation and follow-up be developed and pre-tested and that resources be set aside for designated centers (e.g., environmental/occupational clinics) to respond rapidly in the event of an incident.
