Note for PUBHLTH 324 at UMass(1)
Note for PUBHLTH 324 at UMass(1)
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Date Created: 02/06/15
Public Health 324 Epidemiology 101 History I The early years Hippocrates John Graunt JamesLind John Snow 1 Quafl fying 1159359 The first Provided framework for Conducted the rst Considered one of j Wtr39ilanalge c39emes Epidemiologist modem demography clinical trial the founders of 1 ln jig 12365 Father of Medicine Estimated population growth 12 sailors with Epidemiology Observed that and rate of growth in London Scurvy First on record to I Modern epidemiology disease varies by Natural andPolitical Hypothesis acids assess geographic 1 Chronic diseases location Observations Made upon the prevent scurvy distribution of 39 laws 19305 environment and Bills ofMortality Result disease and try and 1 Healthrelated states behaVior Analysis of mortality rolls Improvements determine cause 1 Methodologic advances since 19505 First to utilize in early modern London observed in group Water pump in systematic Observed trends with age that took oranges London was causing Now observation gender season location and lemons Cholera 1 Re emergence of infectious diseases Epidemiology is the study of causes and distribution of diseases morbidity injuries disability and mortality in populations Epidemiologic studies are applied to the control of health problems in populations I Descriptive determine burden of disease and study natural history of it I Analytical Identify the causes and evaluate new prevention andor treatment ENDEMIC persistent usual expected occurrence of disease or other health related problems in a defined population over a given period of time EPlDEMlC occurrence of disease or other health related problems in a defined population ABOVE THE EXPECTED over a given period of time PANDEMIC 7 epidemic affecting a large number of people many countries continents or regions EXPOSURE 7 factor which may cause outcome suspected cause of outcome OUTCOME 7 health status of interest disease death pregnancy suspected effect of exposure Prevention developed using information regarding risk factors for disease 1 PRllVLARY Diseasefree individuals Prevention BEFORE occurrence I Physical activity condoms supplements 2 SECONDARY Symptomfree diseased individuals EARLY diagnosis I Mammograms cholesterol test pap smear 3 TERTIARY Symptomatic diseased individuals LllVHT disability due to health status I Treatment follow up patient education Descriptive Epidemiology Looking at the distribution of disease in terms of person place and time Hypothesis generating Girls 50 5 Proportion is like percent Proportion xN of chilcren in bike accidents 7 Overall 35100 035 35 7 Envs39 2050 rm 40 GirI5115SO 03 30 Prevalence proportion in a defined population with EXISTING cases Point prevalence speci c date vs period prevalence range of year Incidence Proportion in a defined population with NEW cases Public Health 324 Epidemiology 101 gtgtgt PREVALANCEquot cases of disease in population at speci ed time Prevalence people in population at specified time gtgtgtRISK 0r INCIDENCE or CUMULATIVE INCIDENCE or ATTACK RATE L new quotH 39 popululllm at t Numerator is NEW CASES ONLY Denominator is TUl39AL POPULATION 7 PEOPLE NO LONGER AT RISK Essential to specify time interval gtgtgtNCJDENCE RATE 4 a a Ineldence Rate Pets oilrilne of Il39iSk population Numerator is NEW CASES ONLY Denominator is person time of at risk population Unit is per persontime Ratio is a comparison independent of each other a a mammasvmWnan mn artmt n Falr an x a among have an o r renaminaaasn mahwxuqmmnmmv Odds Ratio Risk Ratio Rate Ratio Rate x events per tN Kit I events FE DIN um po not 1 raftrrnwtem mamas mvaccdarh er ear erlm b m tmgvlqenm o amul tnmrie sI Incidence rate Number ofNEW cases in a de ned population over a DEFINED TJME PERIOD Mortality rate Number of DEATHS de ned population over a DEFJ NED TJME PERIOD Birth Rate Number ofBIRTHS in a de ned population over a DEFJ NED TJME PERIOD Adjusted Rate When comparing rates it is important those populations being compared are similar with respect to factors that might impact disease or death such as age gender education level Persona 39Iime 10D PEISD lVEEE in w e Frnm rA39lfa39 ofttme ur Ian Lecvte 7 ovaw mm more 7 r a W mo mt Public Health 324 Epidemiology 101 Descriptive Study Designs Case Report Detailed account of disease ofan INDIVIDUAL Typically an unusual case Anecdotal can genemte hypothesis Strengths Documents unusual disease cases identify new diseases andor epidemic Limitations no comparison group small sample size mm a m mutt m a mu anawaucv camptumu bv vaclamasta alter mtvauleuno Dsnvtse mm m xwlswu m Dot11min A am we Case Study 7Detailed account of disease of a small group of patients with similar diagnosis also unusual case Anecdotal may provide clues in identifying a new disease or adverse health affect from an exposure Strengths Documents unusual disease cases identify new diseases andor epidemic Weakness no comparison group small sample size Pnelqumlis Pneumonia Los Angeles r M mimic thMn mp u m uttmmt Ma tw mtmlm quotmm trmtt Hum mug mam mm hummus ttu mummmmw TnhvmuwnlumuH llmlaluulnitm tlulHummlml mul Ecological Studies 7 compare disease frequencies in a population based on a factor ofinterest No Data on individual level confounder prone to ecologic fallacy because facts that are true of a group may not hold true on an individual level Strengths inexpensive quick may utilize existing data useful for generating hypothesis Limitation ecologic fallacy does not account for confounder thus cannot link exposure to disease greater number of differences among the population x mm mum Cross Sectional Study 7 prevalence studies measure exposure and disease at same time Strengths individual data important for public health planning useful for generating hypothesis can be conducted quickly and with limited resources Limitation cannot determine if exposure preceded disease cannot determine causality Surveillance 7 continuous monitoring of health events in the population Can be passive using existing data or active nding new reportable cases Simplicity Flexibility Data Quality Acceptability Sensitivity Predictive Value Positive Representativeness Timeliness Stability Use ofDescriptive studies 0 Trend analysis 0 Planning 0 Hypothesis generating Public Health 324 Epidemiology 101 Sources of Data 0 Existing data quick easy cheap large pop Standardized VS incompleteinaccurate may miss people of interest may not have data on necessary variables 0 BirthDeath certi cates 0 Medical records 0 Schoolemployment records 0 New Data quality and better controlled measures variables of exact interest and target population VS costly timeconsuming interviewee quality recall of information falsi ed information o Questionnaires surveys 0 Physical measurements interviews 0 Lab measurements Analytic Epidemiology COMPARE disease incidence in TWO OR MORE groups selected from single population Hypothesis testing whether a given exposure increases or decreases the incidence of a given disease outcome If ratio gt10 incidence is higher among exposed than unexposed If ratio lt 10 incidence is lower among exposed than unexposed gtgtgtRELATIVE RISK Risk of disease anion exposed moup Relatlve Risk Risk of disease among nonexposed group gtgtgtREALTIVE RATE Rate of disease among ex osed 21390quot Relative RateH lkp Rate of disease among nonexposed group gtgtgtODDS RATIO Diseased Exposed DE a Disease unexposed DU b No disease exposed NE c No disease unexposed NU d adbc Your bookie tells you that the odds on a horse are 31 3 Probability of winning mi 34 2 Probability oflosing 5 14 Smoking 3 15 10 25 lt t g 5 20 25 I 50 i Caicdlars the odds oiexpcsure among the 2 Caicuiala me adds ai Exposure among 3 Foiiii a mile diseased giodp nondiseased group Odds Ofexposure in diseased gisdp Probability afexposilre in diseased grallo15i25Probabiidy ulexpnsure m nnnsdiseased gmup5r3925 15izsiiiio25iia Probability OYLDI being exposed in diseased teing exposed in nunsdiseased groupZi ZS Odds gramme in nonsdiseased giuup 5i39257i2U25U 2S Odds rexpnsuie in diseased group Odds ole crime in diseasesfree gioup 153925M io 25i 5 i5izsiir2m25id25 DRii 5 39 10 257 6 D Public Health 324 Epidemiology 101 gtgtgtRISK RATIO Can be used to determine the relationship between exposure and disease aacbbd Risk of disease in exposed Risk of disease in unexposed gtgtgt RATE RATIO iRisk of disease in exposed persontime Risk of disease in unexposed Infectious Disease Caused by pathogen or infectious agent May Occur in Baseline Levels or Outbreaks Can be transmitted to susceptible individuals Susceptibility depends upon genetic background nutritional status vaccination prior exposure DIRECT personperson INDIRECT vehiclehome inanimate vectorborne animal airborne VERTICAL parent to offspring HORIZONTAL among peers Infectivity capacity of an agent to enter and multiply in a susceptible host Pathogenicity capacity of an agent to cause disease in the infected host Virulence severity of the disease Toxigenicity capacity of the agent to produce a toxin or poison Resistance ability of the agent to survive adverse environmental conditions Antigenecity ability of the agent to induce antibody production in the host Public Health 324 Epidemiology 101 Outcomes of Exposure 0 No infection 0 Carrier 0 Subclinical infection 0 Clinical infection Incubation Period Time between infection and first symptom varies by infection and by individual Carrier harbors the pathogen but is asymptomatic Active Immunity Pathogen causes host immune system to produce antibodies against disease Natural previous exposure Artificial vaccine Passive Immunity admission of preformed antibodies Natural placental transmission to fetus breastfeeding Artificial administered Herd Immunity Non immune person is protected if a large proportion of the surrounding population is immune Non susceptible persons dominate Barrier of direct transmission and prevents spread within group Vaccination is important Noti able diseases must be reported sue to seriousness Disease Outbreaks Sudden Cause not clear Need to work quickly Cases exceed number expected Steps in Outbreak Investigations 1 Establish existence of an outbreak Verify the diagnosis De ne and identify cases Describe the outbreak Epidemic curve mode of transmission Develop and evaluate hypotheses Collect additional evidence Implement control and prevention measures Assess status of outbreak WSF MPP N Epidemic Curve Plot of the number of cases y axis by the time at which they occurred x axis Uses of an epidemic curve Estimate incubation time Determine outbreak status Suggest mode of transmission Modes of Transmission Point source A common source over a short period Produces curves with a single peak Personto person Produces curves with multiple peaks Continuous source Produces curves with plateaus
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