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Epidemiology

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concerned with the distribution (frequency of disease occurrence over a population not the individual) and determinants (factors that provoke a change) of health, diseases, morbidity, morality, and disability in populations.

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Epidemiological Description

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describes disease by age groups, time trends, geographic regions, other variables that affect distribution. This is different than the clinical approach which describes disease by symptoms.

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Determinants

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factors that provoke a change in health. Ex. bio agents--bacteria. Chemical agents--carcinogens. Less specific---stress, high fat diet.

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Distribution

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frequency of disease occurrence may vary from on population group to another.

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Morbidity

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illness

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Mortality

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death

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Aims/Goals of Epidemiology

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1. To describe health status of populations (to discover trends of disease occurrence). 2. To explain the etiology of disease to determine causal factors and mode of transmission. 3. To predict disease occurrence (number of cases to project appropriate mitigation measures). 4. To control the distribution of disease (the epidemiological approach is used to prevent the occurrence of new cases of disease, to eradicate existing cases, and prolong the lives living with disease.)

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Epidemic

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the occurrence in a community or region of cases of an illness (or an outbreak) clearly in excess expectancy. an excessive occurrence (prevalence) of a disease. Pandemic refers to an epidemic on a global scale.

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Endemic

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a disease that is habitually present in a particular geographical region.

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Epidemic Threshold

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the minimum number of cases that would support the conclusion that an epidemic is underway.

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John Graunt

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used birth and death data and established trend regularities.

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Edward Jenner

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Small pox vaccine

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Natural Experiments

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the epidemiologist observes changes in an outcome as the result of a naturally occurring situation.

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John Snow

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investigated London's Cholera outbreak and used a natural experiment to find out.

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William Farr

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provided foundation for classification of disease (ICD system). Examined linkage between mortality rates and population density.

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7 Uses of Epidemiology

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1. To study the history of health populations. 2. to diagnose the health of the community. 3. to study the working of health service-operations research. 4. to estimate the individ. risk of disease. 5. to identify syndromes. 6. to complete the clinical picture of chronic disease. 7. to search for causes of health and disease.

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Secular Trends

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(historical use) describes the changes in disease frequency over time.

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Factors affecting reliability of Trends

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1. lack of comparable data over time due to changing diagnostic criteria. 2. aging population 3. changes in the fatal course of the condition.

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Disappearing Trend

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no longer present in epidemic form. Ex: Small Pox

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Residual Trend

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good control not completely effective. Ex: STD's

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Persisting Trend

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not effective treatment or prevention. Ex: Cancer, mental illness.

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New Epidemic

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increasing in frequency. Ex: AIDS, Obesity

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Factors affection population size

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births, deaths, and migration.

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Demographic Transition

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Due to general hygienic and social conditions. Decline in birth and death rate.

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Epidemiological Transition

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is followed by the demographical trans. and describes the shift of infectious disease to chronic diseases.

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Risk Factor

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exposure that is associated with a disease. 1. the freq. of disease varies by the value of the factor e.g., light smoker vs. heavy smoker. 2. it precedes the onset of the disease

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Modern Causality

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strength of the association time sequence consistency upon repetition specificity coherence of explanation

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Biological Gradient

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evidence of dose-response curve: that is an increase in disease risk in increase amount of exposure: Ex. smoking

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Plausability

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if a association is biologically plausible than it will be helpful.

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Experiment: Case-control and Cohort

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experiment that compares people who have a disease (cases) with those who do not have it (controls). People grouped based on variety of exposure and that are followed over time.

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Prepathogenesis

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before agent reacts with host.

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Pathogenesis

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after agent reacts with host

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Primary Prevention

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Occurs during the period of prepathogenesis Passive: does not require any behavioral changes. EX: Fluoridation of water. Active: requires behavioral change. Ex: Vaccinations, smoking cessation.

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2nd Prevention

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Occurs during the pathogenesis phase and includes early diagnosis, prompt treatment, disability limitations.

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Tertiary Prevention

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occurs during the late phase of pathogenesis and includes rehab to restore the patient to functional level.

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Count

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the number of cases of a disease

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Ratio

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the value obtained by dividing one quantity over another. Include: rates, proportions, and percentages.

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Proportion

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the numerator is part of the denominator and could be expressed as a percentage. a/a+b X 100=

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Rate

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a ratio that consists of the numerator and the denominator in which time is part of the denominator. Crude death rate: # of deaths in a year/reference population (midpoint) and use a multiplier of 1,000 or 100,000

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Prevalence

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the number of existing cases of a disease at some designated time.

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Incidence

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the rate of development of a disease in a group over a time period. 1. numerator: the number of new cases 2. denominator: the population at risk

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Attack rate

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different form incidence rate and is often used over a short period of time in response to an outbreak. ill/(ill+well) x 100 (during a time period)

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Interrelationship of P and I

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the P of a disease is proportional to the I rate x the duration D of a disease.

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Specific Rate

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a subgroup of the population that defined in terms of sex, race, age, or single cause of death.

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Adjusted Rate

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rate of morbidity or mortality in which statistical mechanisms have been applied to allow fair comparisons across the population by removing the the effect of differences in composition of various populations.

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Indirect age-adjusted

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A=age group B= total estimated population C=death rate in standard population D=expected number of death in interest population D= (total estimated population(B) * death rate in standard population(C)) / 100,000

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Direct age-adjusted

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Need to determine rate first (C) ((A) Deaths/ (B) Population)*100,000 =C (C) rate* (D) standard population/100,000=age-adjusted for death

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Why is age-adjustment important?

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allows the investigator to make fairer comparisons between different age groups. For instance, the older populations might have higher frequencies of disease simply because they are older which could lead to misinterpretation of data.

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Direct Adjusted Rate

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used if age-specific death rates in a population to be standardized are known and a suitable standard population is available.

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Indirect Adjusted Rate

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If age-specific death rates of the population for standardization are unknown or unstable, for example, because the rates to be standardized are based on a small population. Use SMR (Standard Mortality ratio)

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Standard Mortality Ration (SMR)

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observed deaths/expected deaths x100

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Interpretation of SMR

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if observed and expected number are the same: SMR =1.0 or 100% SMR = 2.0 than the death rate is two times greater than the expected. Less, then the observed are fewer. More, the observed is greater.

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Descriptive Studies

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used to identify a health problem that may exist. Characterize the amount and distribution of disease.

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Analytic studies

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follow descriptive studies, and are used to identify the cause of the health problem.

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Positive declaration

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Research hypothesis. Ex: the infant mortality is higher in one region that another.

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Negative Declaration

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Null hypothesis. Ex: there is NO difference between the infant mortality rates of two regions.

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Implicit Question

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to study the association of....whatever.

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The method of difference

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all the factors are the same expect for a single factor. Thus, the variable. Ex: the study of the role of physical activity in reducing morbidity of CHD.

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The method of agreement

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a single factor is common to a variety of different settings. Ex: wherever there is air pollution there is an increase in COPD.

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The method of concomitant variation

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frequency of disease corresponds to dose.Ex: smoking, the more one smokes the greater the risk.

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The method of residues

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subtracting potential causal factors to find factor(s) with greatest impact. Ex: multiple regression analysis used to determine the number of risk factors associated with CHD.

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The method of analogy

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The mode of transmission and symptoms of a disease of unknown etiology bear a pattern similar to that of a known disease.

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infant mortality

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used for international comparisons; a high rate indicates unmet health needs and poor environmental conditions.

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3 Approaches of Des. Epi

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Case Reports (cases) Case series (summarize the characteristics of patients from a clinical settings.) Cross-sectional studies. ( surveys of the population to estimate the prevalence of a disease or exposure.

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The importance of characteristics of person, place or time

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person, place or time can directly or indirectly affect the occurrence of disease because they affect a wide variety of exposures associated with lifestyle, behavioral patterns, access to medical care and exposure to environmental hazards.

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descriptive studies

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are concerned with characterizing the amount and distribution of diseases in a population.

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analytical studies

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are concerned with determinants of disease, reasons for high or low frequency of disease in a specific subpopulation

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Ch of Person: Age

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most important when describing age because age-specific disease rates show greater variation than rates defined by any other personal attribute.

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4 reasons for age associations

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1. the validity of the diagnosis: affected by classification errors. 2. Multimodal Trends: meaning that there are peaks and declines in the frequency of diseases at different ages. 3. Latency effects: between environmental exposures and and the development of the disease. Ex. Cancer 4. human biological clock: immunity wanes and increased cell division.

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Ch of person: marital status

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married people have lower rates of morbidity and mortality.

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marital status hypothesis

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Protective: may provide an environment that is conducive to health. Selective: people who marry may be healthier to begin with.

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health migrant effect

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observation that healthier individuals, typically younger persons form the majority of migrants.

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Socioeconomic status

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excess mortality and morbidity. Factors include poor housing, crowdedness, low income, racial disadvantage, poor education, etc.

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Measurement of Social Class

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Prestige of occupation, educational attainment, income.

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Social causation (breeder hypothesis)

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conditions arising from membership of low social class groups produce mental illnesses.

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downward drift hypothesis

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the clustering of psychosis will drift down to lower classes.

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Ch of Place

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Internationally: Differences in infectious disease, climate, culture. WHO tracks this. Geographic: variation within a country. Urban/rural difference: urban diseases are due to overcrowding pollution and poverty. Localized occurrence of disease. person-to-person diseases found in urban areas.

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Geographical Information Systems (GIS)

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a method to provide a spatial perspective on the geographical distribution of health conditions.

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Reasons for place variation in disease

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Gene/environment interactions. Influence of climate environmental factors: ex; chemical agents linked to cancer.

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Ch of time

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cyclic fluations point epidemics secular time trends Clustering

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cyclic fluctuations

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more accidents in the summer and flu in the winter

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Clustering

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unusual aggregation of health events grouped together in time and space. Temporal: post vaccinations Spatial: concentration of a disease in a specific geographical area.

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Secular time trends

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gradual changes in frequency of a disease over long periods of time.

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Point epidemic

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the response to a group of people circumscribed in a place and time to a common source=of infection or contamination and exposed simultaneously.

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Quality and use of Epi data

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nature of data availability of data completeness of population coverage strengths vs. limitations

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Nature of data

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the type of data: vital stats, cases, etc. makes conclusions about inferences that can be made.

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availability of data

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the investigator's access to data

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Completeness of population coverage

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Representativeness: aka external validity: refers to the generalizability of findings to the population from which the data have been taken. Thoroughness: how detailed is it.

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Strengths vs. limitations

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the utility of data for various types of epi research.

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Pres. #1: Assessment of 2010 global measles

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the WHO endorsed a goal of reducing measles mortality by 90% over the course of 10 years. The conclusion was that this goals was not met due to India and outbreaks in Africa. MCV1=measles containing vaccine.

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Pres. #2: Mortality and Hospital stays with MRSA and EC

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purpose was to estimate the impact of morbidity mortality and demands on health care services of antibiotic resistant strains of MRSA and EC. Concluded that there was excess mortality with BSI's caused by MRSA and Ec, thus prolonging hospital stays and imposes a burden on the healthcare system.

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Pres. #3: Sport-related brain injury

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the purpose was to determine the incidence, nature and severity of sport-related injuries in the general population.

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Pres.#4: Advanced Parental Age and the Risk of Autism Spectrum Disorder

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Purpose was to evaluate the effects of maternal and parental age on the risk of autism spectrum disorder. It used a cohort case design. Concluded that ASD risk increases with both maternal and parental age and decreases with birth order.

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Pres. #5: adverse effects in young adult reporting use of energy drinks and caffeine

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Purpose was to assess the prevalence of psychological and behavioral adverse effects among young adults in ER patients who reported drinking caffeine or energy drinks prior to ER admission. Concluded that those who consumed energy drinks had higher report of adverse effects compared to those who only drank caffeine drinks.

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descriptive studies

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cross-sectional surveys used to depict and individual's health characteristics with respect to time place and person. Hypothesis generation

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analytical studies

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ecological studies, case-control studies, cohort studies. used to test specific etiological hypothesis. Hypothesis testing

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Experimental study

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has the greatest control of the research study by which the investigator can manipulate the subject and the variable.

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Ecologic study

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examines a group as the unit of analysis insofar as other studies use the individual as the unit of analysis. Ex: a study of mortality from lung disease in different cities that are known to have differing levels of air pollution would comprise a ecologic study. The unit of analysis is the city. Limitations: the ecologic fallacy Important: the level of exposure for each individual in the unit being studied is unknown.

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Ecologic comparison study

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examines exposure and disease rates among different groups over the same time period.

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Ecologic trend study

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examines the correlation of changes in exposure and disease within the same community, country or other aggregate unit.

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Ecologic Fallacy

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Observations made at the group level. may not represent the exposure-disease relationship at the individual level. The ecologic fallacy occurs when incorrect inferences about the individual are made from group level data.

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Cross-sectional study

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a type of descriptive study designed to estimate the prevalence of a disease or exposure. AKA prevalnce study Advantages: less time consuming that case-control or cohort studies inexpensive good, quick picture of prevalence of exposure and prevalence of outcome Disadvantages: difficult to determine the temporal relationship between exposure and outcome (lacks the element of time) may have excess prevalence from long duration cases (such as cases that last longer than usual but may not be serious).

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uses of cross-sectional study

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Hypothesis generation Intervention planning Estimation of the magnitude and distribution of a health problem Limitations: because of a relative lack of utility for studies of disease etiology. Does not provide incidence data. Cannot study low prevalence of diseases (e.g., mental illness) Cannot determine temporality of exposure/disease.

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Case-control study

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a type of analytical study that compares individuals who have a disease with individuals who do not have the disease in order to examine differences in exposures or risk factors for the disease. Advantages: relatively inexpensive. less-time consuming than cohort studies. can evaluate effects of multiple exposures. efficient for rare outcomes or outcomes with long induction or latency periods. Disadvantages: subject to recall bias (based on subject's memory and reports). inefficient for rare exposures. difficult to establish clear chronology of outcome and exposure.

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Interpretation of OR (odds ratio)

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OR=1.0: the odds of exposure are equal among the cases and controls thus, is not a risk factor therefore no association. OR=2.0: suggests that the cases were twice as likely as the controls to be exposed. OR= <1.0: suggests it is a protective factor.

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Cohort

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a population group that is followed over a period of time

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Cohort Studies

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a type of analytical study that collects data and follows a group of subjects who received a specific exposure. The incidence of a disease or outcome of interest is tracked overtime. The incidence in the exposed group is compared with the incidence in groups that are not exposed, have different levels of exposure, or have different types of exposures. Advantages: Can evaluate multiple effects on a single exposure. More efficient rare exposures and outcomes with long induction or latency periods. Can directly measure incidence. Clear chronological relationship between exposure and outcome. direct determination of risk can study multiple outcomes can study rare exposures Disadvantages: Expensive. Time-consuming. Inefficient for rare outcomes with long induction or latency periods. Subjects lost over time thus no more follow-ups.

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Population Based Cohort

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the cohort includes the entire population or a representative sample of the population. Framingham Study: Cohort study of CHD exposure=unknown until 1st period of observation Advantages: Can be generalized over the entire population Disadvantages: not efficient for rare exposures.

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Exposure Based Cohort

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subjects with a common exposure (occupational) Ex. Workers exposed to lead paint Weakness=rare exposure

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types of temporal cohort studies

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prospective, retrospective and historical prospective

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prospective cohort study

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determines levels of exposure at baseline (present) and follow up for occurrence of disease at some time in the future.

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advantages of prospective cohort studies

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enables to collect data on exposures the size is under control of the investigator bio and physio assays can be done with less concern of the outcome being affected by the course of the disease direct measures on the environment

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Retrospective cohort study

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use historical data to determine the level of exposure at some baseline from the past

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advantages of retrospective cohort studies

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do not have to wait for follow-up collections of data with saves time. Its cheaper to use the data that is already collected and possibly could be quite extensive data.

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cohort study: measure of association-relative risk

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direct measure of association of exposure and outcome

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relative risk

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is the ratio of the incidence of the disease in the exposed group to the incidence of the non-exposed group.

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nested case-control study

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type of case-control study in which cases and controls are drawn from the population in a cohort study that population then comprises both exposed and non-exposed persons.

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advantages of nested case-control studies

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have control over confounding factors reduced cost b/c exposure information is collected from a subset of the cohort only e.g., suicide among electricity workers

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strengths of cohort studies

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direct determination of risk timing sequence of exposure and outcome can study multiple outcomes can study rare exposures

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weaknesses of cohort studies

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takes a long time costly subjects lost to follow-ups

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Clinical trial

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a carefully designed experimental investigation of the effects of a treatment or technology that uses randomization, blinding of subjects to study conditions, and manipulation of the study factor.

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ecologic study

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a type of descriptive study that assesses the correlation (association) between exposure rates and disease rates among different groups or populations over the same time period. The unit of analysis is the group. Ex: a study of mortality from lung disease in different cities that are known to have different levels of air pollution would comprise an ecologic study. The city is the unit of analysis. Advantages: Inexpensive. Less-time consuming. simple and easy to understand. examines community, group, or national level of data or trends. generating hypothesis Disadvantages: ecologic fallacy, which infers association of the the population level. Difficult to detect complicated exposure-outcome relationships.

Epidemiology for Public Health Practice MidTerm – Flashcards

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