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Environmental Health III. Epidemiology

Environmental Health III. Epidemiology. Shu-Chi Chang, Ph.D., P.E., P.A. Assistant Professor 1 and Division Chief 2 1 Department of Environmental Engineering 2 Division of Occupational Safety and Health, Center for Environmental Protection and Occupational Safety and Health

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Environmental Health III. Epidemiology

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  1. Environmental Health III. Epidemiology Shu-Chi Chang, Ph.D., P.E., P.A. Assistant Professor1 and Division Chief2 1Department of Environmental Engineering 2Division of Occupational Safety and Health, Center for Environmental Protection and Occupational Safety and Health National Chung Hsing University

  2. Outline • Definition • Epidemiology • A classic example • Modern environmental epidemiology (EE) • Major challenges • Conduct of an EE studies • Case studies

  3. Definition and results • The study of the effect on human health of physical, biological, and chemical factors in the external environment, broadly conceived. By examining specific populations or communities exposed to different ambient environments, it seeks to clarify the relationship between physical, biological, or chemical factors and human health. (National Research Council, 1991) • Not cause-consequence type results but the association or relationship • Example: ionizing radiation

  4. A classic example • Dr. John Snow’s study on cholera transmission in London • Observation and Hypothesis • Why a classic • Recognized the association • Formulated a hypothesis • Collected information • Alternative explanation • Minimized the effects of alternative explanation • Minimized the collection of biased or false information

  5. Modern environmental epidemiology (EE) • Disease-centered to exposure-centered • Basic criteria • Strength and specificity of the association • Consistency of findings • Existence of a dose-response gradient • Biological plausibility • Coherence of the evidence • Supporting experimental, or quasi-experimental, evidence

  6. Modern environmental epidemiology (EE) • Design of an epidemiologic study • Cohort study: WWII atomic bombing • Case-control study: like cigarette and lung cancers • Difference between cohort and case-control • Based on whether they have been exposed or having the disease being evaluated

  7. Modern environmental epidemiology (EE) • Prospective cohort • Retrospective cohort • Case-control • The disease has not occurred at the time the exposed and non-exposed groups are defined • The disease has occurred at the time the exposed and non-exposed groups are defined • Past history of exposure is the primary info collected. Could be relatively short • Usually relatively long study • Evaluation of a number of exposure in relation to one disease • One exposure is evaluated to a number of disease.

  8. Major challenges • Exposure assessment • Health endpoints • Potential bias

  9. Challenge 1 Exposure assessment (I) • Valid environmental measurement and accurate estimates are essential

  10. Challenge 1 Exposure assessment (II)

  11. Challenge 2 Health endpoints • In the past, mortality and morbidity • Environmental agent to the quality of life. Therefore, biochemical, physiological, and neurological agents • Measurement • Two broad groups • Measurement of psychological or psycho-physiological functions • Measures of mental state and behavior • Recently, biological markers – cellular or molecular indicators • Toxic exposure • Adverse health effects • susceptibility

  12. Challenge 3 Potential biases • Three categories of biases • Selection bias: deficiencies in study design • making selection before the disease has occurred. • Observation bias: deficiencies in study design • Cohort: interviewers do not know the exposure status of studying individuals • Case-control: neither the patient nor the data collector knows the diagnosis • Confounding bias: inevitable • An evaluation of two variables is influenced by a third variable that is a cause of the disease and also associated with the exposure.

  13. Developing of Molecular Epidemiology • Molecular technology to measure exposure, early biological response, or host characteristics • Marker and effect correlaiton • Examples • Monoclonal antibody • Cotinine in blood • Benefits • Human risk prediction • Early identification of carcinogenic agents • Subgroup population risk • Genetic susceptibility • Increased analytical sensitivity and continuous monitoring

  14. Conduct of an EE studies • Population group, e.g. workers • Contacts • Guarantee their interest • Joint training • Visit the subject at home • Single lab • Consent or permission for intrusive tests • Confidentiality • Impact of computer • Reconsider the correlation, reasonable?

  15. Case studies • Fluoride in drinking water and dental caries • Cigarettes and lung cancer • Ionizing radiation and cancer • Electric and magnetic fields and leukemia

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