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)