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 National Chung Hsing University

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

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

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

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

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

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.

Major challenges Exposure assessment Health endpoints Potential bias

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

Exposure assessment (II) Challenge 1

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 Challenge 2

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. Challenge 3

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

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?

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