PRINCIPLES OF TOXICOLOGY - Biology East Borneo

21 Epidemiologic Issues inOccupational and EnvironmentalHealthEPIDEMIOLOGIC ISSUES IN OCCUPATIONAL AND ENVIRONMENTAL HEALTHLORA E. FLEMING and JUDY A. BEANEpidemiology is the study of the distribution and determinants of disease or death in humanpopulations. In the case of the environment or the workplace, epidemiology attempts to determineassociations between a chemical exposure and particular human health effects.This chapter will discuss:• What epidemiologists study, and describe the scientific discipline of epidemiology• Epidemiologic causation, its implications for other scientific disciplines, and the interpretationof the results of epidemiologic studies• Types of epidemiologic studies, and advantages and disadvantages• Definitions of exposure, disease, population, and their measures in epidemiologic studies• Types of measures of risk in epidemiologic studies• Bias and other issues, and how to approach these issues in epidemiology• Occupational and environmental epidemiologic issues21.1 A BRIEF HISTORY OF EPIDEMIOLOGYOver 2000 years ago, the famous Greek physician Hippocrates noted that environmental factors caninfluence the occurrence of disease. However, until the nineteenth century no one measured thedistribution and determinants of disease or death in human populations in a formal way. In particular,John Snow in 1855 noted a possible association between drinking water and deaths from cholera inLondon. Using epidemiologic principles (not defined as such at the time), Snow showed that cholerawas spread by contaminated water, long before the bacterial organism for cholera had even beendiscovered. His work lead to public health interventions to prevent the spread of cholera.The data, which Snow (1855) used to perform this investigation, form the basic building blocks ofan epidemiologic study. He collected information based on a case definition of the disease (i.e., deathdue to cholera), a definition of exposure (i.e., drinking water source), and a definition of thedenominator population (i.e., the total number of at risk people living in the particular district). Snowused this information to construct a standard rate or risk for comparison: the number of cholera deathsassociated with a particular type of drinking water divided by the number of at risk people living inthat particular district. Thus, he was able to compare the rates (or risk) of cholera deaths by the differentwater supplies (Table 21.1).Snow’s investigation also illustrates some common sources of epidemiologic data. These includevital records (deaths, births, etc.), Census data and questionnaires (source of drinking water). OtherPrinciples of Toxicology: Environmental and Industrial Applications, Second Edition, Edited by Phillip L. Williams,Robert C. James, and Stephen M. Roberts.ISBN 0-471-29321-0 © 2000 John Wiley & Sons, Inc.511