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.

Environmental Health III. Epidemiology

Shu-Chi Chang, Ph.D., P.E., P.A.Assistant Professor1 and Division Chief2

1Department of Environmental Engineering2Division 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