environmental health iii. epidemiology shu-chi chang, ph.d., p.e., p.a. assistant professor 1 and...
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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