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CLASS 4 - Theory.doc

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Margareth Zanchetta

Chapter 9 EPIDEMIOLOGYEpidemiology defined as the study of the occurrence and distribution of healthrelated statesevents in specified populations including the study of the determinants influencing such statesthe application of this knowledge to control the health problem It s purpose is to describe explain predict and control challenges to population healthEpidemiologists seek healthrelated events by answering questions who what where when and by following trends in the population They also examine causalitymodes of transmission Then controls are established to prevent new illnesscure if possible and rehabilitateprevent complications Subdisciplines can be divided into twostreams1 The exposureoriented subdisciplines eg nutritional social environmental2 The diseaseoriented subdisciplines eg cancer injury prenatal Some subdisciplines have less clear categorizations such as occupational or molecular epidemiologyHistory Background of Epidemiology Hippocrates was the first to noticerecord a possible relationship btw the environmenthealthdisease of people and suggested that physicians study the mode in which the inhabitants livewhat are their pursuits whether they are fond of eatingdrinking to excessgiven to indolence lethargy or are fond of exerciselabournot given to excess in eatingdrinkingJohn Graunt was the first to study statistics of epidemics and noted for instance gender differences in births more males than females seasonal variations in deathshigh levels of infant deathsDr Farr initiated a more complete gathering of statistical datawas able to compare death rates among workers in diff types of jobsbtw prisoners and rest of populationDr Snow noticed relationship btw cholera deathssource of drinking waterNightingaleduring Crimean War discovered conditionsmethod of recording deathstheir causesIn 1900 it became evident that although vital statistics of deathillness were important following populations for a period of time to ascertain the progression of various diseasestheir tx was also importantAs medical scientists discoveredimplemented new tx the primary causes of death changed over time from predominantly contagious diseases to chronic illnesses that were influenced by lifestyle behaviours Basic Building Blocks of Epidemiology hosScience of Epidemiologys building blocks include epidemiologic model the concept of susceptibility modes of transmission natural hxprogress of disease associationcausationenviragenonweb of causationEpidemiologic Model contains the elements of host agentenvironmentModel is frequently presented as a triangle posits that disease is the result of the interaction of these threeHost human being in which the disease occursAgent contagiousnoncontagious force that can being or prolong a health problem eg bacteria virusesas well as stimuli such as smoking or absence of Vit CEnvironment context that promotes the exposure of the host to the agent Gordisvector is defined as a factor that moves btw the agent and the host assisting the movement of the disease btw the other two elementsTimmreck added the concept of time to the model Harkness noted that using a Venn diagram instead of triangle emphasized the interrelatedness within the model because with Venn overlaps existGenetic Profile family hx sex age race occupation religion Environmental Characteristicsmarital stat immune Agent typesPhysical weather geography systempollutionbiologicinfectious virus bacteria fungi chemical smoke poison Biological plants animals physical heat nutritional microorganismslackexcess psychological stressSocial neighbourhood housingEpidemiologic Variables in order to completely accurately describe the patterns of health workchallenges the descriptive of epidemiology are used These are the named person placetime Within each variable are factors that further describe the event eg under person one might look at age diff sex ethnicity genetics immune status marital stat immigrationOther environmental influences for the person education socioeconomic status occupationIndividual characteristics such as dietary practices use of alcohol physical activity may be helpful eg under time considers characteristics such ascyclic or seasonal variation of a health event healthchallenges following specific events such as postpartum depression or time trends increase of chronic diseaseover time eg under place include variation btw regions countriescontinents population density ruralurban or working in a particular building or living close to cataclysmic event such as ChernobylSusceptibilityCombination of characteristics of each individual within that host group interacting with the factors present or absent in the other elements of the epidemiologic triangle determines the rik or degree of susceptibility of each person to a particular agentSusceptibility and risk can also be described as vulnerability which determines the individual host responseThe answers to the personplacetime questions while pointing to group susceptibility can also point to group protectionEg we may discover that one or more of the characteristics studied ageactivity may mitigate some of the effects of other characteristicsThe Venn diagram above identifies factors that may incdec the risk of susceptibility of the host to the disease Some factors may be modified lifestyle while others are not under the individuals control age genderModes of transmission Two main modes of transmission directindirect1 Directcontact btw the person with the disease and another person through touching skinskin sexually2 Indirect involves a common vehicle that moves the disease to the new host eg lake
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