Lecture 6: environmental and occupational epidemiology
bias
deviation of data from the truth- occurs when the relationship between exposure and sieges in study population does not represent true relation between exposure and disease in general population because the investigator selected study pop in an unrepresentative manner
Confounding
distortion of exposure-disease relationship by a third variable that is associate both with exposure and with disease
environment
domain that disease causing agent may exist "all that which is external to individual human health"
Characteristics (and contributions) to environmental health from epidemiology
-Concern with populations- in contrast to clinical medicine -population medicine use of observational data: avoid ethical dilemmas with human experiments using intervention treatments -Methodology for study design- the characteristic study designs of epidemiology are well-suited to answering questions relating population level health effects of environmental phenomena -Descriptive and analytic studies: two basic types of epidemiological studies serve different and complementary purposes
Contributions of epidemiology (4)
-Environmental epidemiology: the study of disease and health conditions (occurring in a population) that are linked to environmental factors -we study and perform experiments in environmental and occupational epic to investigate the human population level effect of environmental contaminants/other hazards -john snow is the father of epic- investigated cholera outbreak -observational -Percival Pott- first person to observe and describe environmental cause of cancer; observation of chimes sweep workers having more scrotal cancer than non chimney works left to first environmental health policy (bath once per week)
Hills criteria of causality (correlation does not imply causation)
-strength is association: causal factor and sieges outcome strong -consistency in findings specificity of association: gin diseases from given exposure temporality: cause precede effect Bio gradient: dose response strengthens relationship bio or theoretical plausibly: makes sense coherence with established knowledge
causality
an existing association between an agent fact and disease in host
why is the epi triangle important
because it helps describe causality of infectious disease as well as its framework for organizing causality in other environmental problems
two main classes of epic studies
descriptive and analytic
Cohort studies
classifies subjects as exposed or non exposed (both disease free) and follows and observes disease inside or mortality rates; retrospective or prospective
intervention study definition and the two types
considered an analytic study- designed to test outcomes associated with intentional changes in status of research subjects (ex: clinical trial) Randomized Control Trail: manipulates an exposure variable and randomly assigns subjects to either a treatment or control groups- typically use RCT to test the efficacy of new meds, vaccines etc Quasi experiment: similar to RCt but does not randomly allocate individuals to study groups due to constrained imposed by pic health programs- x: to fluoridate water supply or not
descriptive study:
description of the occurrence of disease in populations according to classification by person, place, and time variable. Can also serve the purpose of fathering info-to prove a basis for more in depth:
agents
factors (microorganisms or form of radiation) presence or excessive presence of absence is needed for disease to occur
health worker effect
form of selection bias- occurs when workers are compared to general population- there is bias against finding adverse health effects among workers (workers are healthier normally than general population n)
analytic study
hypothesis driven studies, oberserational/intervention: examines causal (etiologic) hypotheses regarding association between exposure and sieges, i.e. cohort, case control, cross sectional
cross sectional
known as prevalence studies- measures disease and exposure at same time
Incidence
new- rate of new problem during time period and the duration of the problem
prevalence
old and new- proportion of the population with problem at a designated time - to calculate: number of individuals in population with disease at given time/ number of individuals in the population at risk of developing the disease at a given time
Host
person or living animal that is a host to an infectious agent under natural conditions i.e. mosquito
case control
starts with disease (case) and non diseased (control) groups and looks backwards in time- can ask about their exposure
latency period
time interval between initial exposure to disease causing agent and manifestations in host- LP can affect epidemiologists ability to definitively ID outcomes of exposure (environmental caused diseases often have long latency periods)