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What is Epidemiology?

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- is the study of how often diseases occur in different groups of people and why - is the study of the distribution and determinants of health problems in specified populations and the application of this study to control health problems - is concerned with the distribution and determinants of health and diseases, morbidity, injuries disability and mortality in populations - Epidemiology studies are applied to the control of health problems in population

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Key Characteristics of Epidemiology

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- population focus, distribution, determinants, outcomes, quantification, and control of health problems

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Population focus

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- all the inhabitants of a given country or area considered together - population medicine: population approach , not a clinical approach

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Populations in Epidemiology

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- neighborhood, city county state territory or country, school, inpatient or outpatient healthcare facility, the global community

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Distribution

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- the occurrence of diseases and other health outcomes varies in populations with some subgroups of the populations more frequently affected than others

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Determinants

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- any factor that brings about change in a health condition or other defined characteristic - causes=factors - could be risk or protective factors

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Exposures

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- contact with disease- causing factor or to the amount of the factor that impinges upon a group or individuals

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Outcomes

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- all the possible results that may stem from exposure to a causal factor - expressed as types and measures of morbidity and mortality - Morbidity: illness due to a specific disease or health condition - mortality: death

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Quantification

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- refers to counting the cases of illness or other health outcomes - means the use of statistical measures to describe the occurrence of health outcomes as well as to measure the association with exposures - Epidemiology is a quantitative discipline

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Control of health problems

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- Natural history of disease: the course of disease from its beginning to its final clinical endpoints - three modes of prevention are directed toward the periods of pre-pathogenesis and pathogenesis: Primary: before the disease occurs Secondary: during the progression of the disease Tertiary: during the later stages of the disease

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Skills acquired through training in epidemiology

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- use of the interdisciplinary approach, use of the scientific method, enhancement of critical thinking ability, use of quantitative and computer methods, communication skills, inculcation of aesthetic values

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Interdisciplinary approach

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- includes: Mathematics and biostatistics (for quantitative methods), History (historical accounts of disease), Sociology (social determinants of disease), Demography and geography (population structures and location of disease outbreaks), Behavioral sciences (models of disease;design of health promotion programs), Law (examining evidence to establish causality ; legal bases for health policy)

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Scientific Method

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- utilizes the following fields: cross-sectional, ecologic, case-control, cohort

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Enhancement of critical thinking ability

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- includes: Reasoning by analogy, making deductions, solving problems

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Quantitative and computer methods

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- Biostatistics is the core discipline of epidemiology - Through training, acquire quantitative skills such as tabulation numbers of cases, making subgroup comparisons, and mapping associations between exposures and outcomes

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Communication skills

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- Epidemiology is an applied field - Information from epidemiologic analyses used to control diseases, improve health in the community, evaluate intervention programs, and inform public policy - Need to disseminate information for controlling health problems/ improving health

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Inculcation of aesthetic values

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- The writing of great thinkers- Hippocrates and John Snow- compelling great works of literature - Other writings: The Jungle (Upton Sinclaire) describes deplorable sanitary condition in Chicago slaughterhouses in 1906; The Plague (Camus) describes the ravages of the disease

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Applications of Descriptive and Analytical Methods to an Observational Science

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- Epidemiology is an observational science that capitalizes upon naturally occurring situations in order to study the occurrence of disease

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Descriptive Epidemiology

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- refers to epidemiologic studies concerned with characterizing the amount and distribution of health and disease within a population - Covers time, place and person (who, where, when and what) - Usually used to generate hypothesis

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Analytic Epidemiology

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- examines causal (etiologic) hypotheses regarding the association between exposures and health conditions (how/why) - Used to test hypothesis - Usually, descriptive studies precede analytic studies - Approach of analytic epidemiology is to take advantage of naturally occurring satiations or events in order to test causal hypotheses.

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Natural experiments

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- naturally occurring events - Naturally occurring circumstances in which subsets of the population have different levels of exposure to a supposed causal factor in a situation resembling an actual experiment, where human subjects would be randomly allocated to groups

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True or False: Epidemiology cannot prove that a particular exposure causes a particular outcome

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True

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True or False: Epidemiology provides sufficient evidence to take appropriate control and prevention measures

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True

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How does Epidemiology differ from clinical medicine?

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- Clinical medicine: Health of an individual, treating and caring for individuals, treating patients based on scientific knowledge , experience, and clinical judgement - Epidemiology: Health of a population - "population medicine", Identifying sources or exposure that affects the entire population, Using descriptive and analytical studies to recommend public health actions for the prevention and control of negative health outcomes

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History of epidemiology

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- Key events include: Bubonic plague epidemics (medieval period), Development of toxicology and biostatistics, development of smallpox vaccine, 1918 influenza pandemic , Identification of smoking as a cause of cancer, eradication of smallpox

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Hippocrates

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- Greek authority departed from superstitious reasons for disease outbreaks - Wrote On Airs, Water, and Places - Suggested disease might be associated with enviromental factors not miasm (cloud that hung low to the earth's surface)

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Black Death

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- occurred between 1346-1352 - of great significance in epidemiology - Thought to be caused by a bacterial infection of Yersinia pestis transmitted via flea bites - Claimed to up to one-third of population of Europe (20 to 30 million out of 100 million people) - Characterized by: swollen lymph nodes, fever, appearances of black splotches on the skin

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Paracelsus

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- founder of the field of toxicology - Introduced concept of: Dose-response relationship, Notion of target organ specificity of chemicals

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John Graunt

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- Published Natural and Political Observations mentioned in a Following Index, and Made Upon the Bills of Mortality- recorded descriptive characteristics of birth and death data , seasonal variations of mortality and compared gender mortality - First to employ quantitative methods - Known as the Columbus of statistics due to his contributions to vital statistics

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Ramazzini

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- Founder of the field of occupational medicine - Pioneer of ergonomics - He authorized De Morbis Artificum Diatriba (Disease of Workers), published in 1700- highlighted the risks of chemicals, dusts and metals in a workplace

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Sir Percival Pott

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- First person to describe an environmental cause of cancer - Observed that chimney sweeps had high incidence of scrotal cancer

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Edward Jenner

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- developed a method for smallpox vaccination in 1796 - Created a vaccine by using material from the arm of a dairymaid, Sarah Nelmes, who had cowpox - 1976-vaccine was injected into a arm of an eight year old boy (James Fipps)

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Johns Snow

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- Father of Epidemiology - Conducted investigation of a cholera outbreak in London - Focused on Broad Street neighborhood - Used both descriptive and analytical epidemiology - Plotted cholera deaths in relation to a pump that he hypothesized as a source of outbreak

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Snow's natural experiment

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- Two different water companies supplied water from the Tames River to houses in the same area - In 1852, the Lambeth Company relocated its sources of water to a less polluted portion of the river - Snow noted that during a later cholera outbreak in 1854, those residents served by the Lambeth Company had fewer cases of cholera than residents served by the other water company (Southwark and Vauxhall Company)

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Snow's contributions

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- Used powers of observations and written expression - Applied of epidemiological methods - Used mapping (spot maps of cases) - Used data tables to describe infectious disease outbreaks - Participated in a natural experiment - Recommended a public health measure to prevent disease (removal of a pump handle)

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William Farr

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- Appointed "Compiler of Abstracts" - chief statistician in England - Developed a more sophisticated system for codifying medical conditions - Used data such as census reports to study occupational mortality - examined possible linkage between mortality rates and population density (defined as number of persons per square mile)

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Robert Koch

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- verified human diseases caused by specific organisms isolated the bacteria that causes anthrax (Bacillus anthracis) and cholera (Vibrio cholera) - Identified the cause of tuberculosis (Mycobacterium tuberculosis)

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Koch Postulates

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- Four postulates that show an association between microrganism and disease 1. The organism must be observed in every case of the disease but not in healthy animals 2. It must be isolated and grown in pure culture 3. The pure culture must, when inoculated into a susceptible animal, reproduce the disease 4. The organism must be observed in, and recovered from, the experimental animal

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Pandemic influenza

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- Spanish flu - Killed 50 to 100 million persons globally - Estimates suggest that one-third of the world's population became affected and developed clinically observable illness

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Discovery of Penicillin

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- Alexander Flemming discovered the anti-microbial properties of the mold Penicillium notatum in 1928 - Antibiotic became available toward the end of WWII.

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Recent innovations

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- Frammingham Study (ongoing since 1948) investigates risk factors for coronary heart disease - Epidemic Intelligence Service (DIS) - Publication of U.S. Surgeon General's support, Smoking and Health (1964) identified deleterious effects of smoking upon health - Smallpox eradication

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Discovery of the following associations:

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- Human papillomavirus and cervical cancer - Bacterium (Helicobacter pylori) and peptic ulcers - Genetic factors and cancer

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Historical use

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- study of history of health of populations

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Community health use

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- diagnose the health of the community and the condition of the people, to measure the true dimensions and distribution of ill-health in terms of incidence, prevalence , disability and mortality

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Health services use

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- diagnose the health of community - to study the working of health services with a view to their improvement - sample application: operational research

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Risk assessment use

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- estimates individual 's risk of disease, accident, or defect - To estimate from the group experience what are the individual risks on average of disease, accident and defect, and the chances of avoiding them

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Risk

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- the probability that an event will occur a risk factor is an exposure that is associated with a disease, morbidity, mortality, or adverse health outcome - Risk assessment is a methodology used to provide - quantitative measurements of risk to health

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Disease causality use

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- search for the causes of health and disease by computing the experience of groups defined by their composition, inheritance and experience, their behavior and environments - one of the most important uses in epidemiology

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True or False: The Historical Use of epidemiology documents the patterns, types, and causes of morbidity and mortality over time

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True

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Epidemiologic Transition

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- Describes a shift in the patterns of morbidity and mortality from causes related primarily to infectious and communicable diseases to causes associated with chronic, degenerative diseases

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Demographic Transition

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- The epidemiologic transition which is a shift from high birth rates and death rates found in agrarian societies to much lower birth and death rates in developed countries

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Steps 1,2,3, and 4 of Presentation of Epidemiologic Data

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- Steps: 1. Checking for accuracy and completeness(data cleaning) 2. Counting and tabulating cases A clean dataset contains a group of related data that are ready for coding and analysis 3. Tabulate the data (simplified because of computers) Frequency tables for categorical variables (sex, race/ethnicity) 4. Graphical presentations - Bar char, line graph, pie charts - Summarize key aspects of a data set (categorical variables) - Visually appealing and intuitive but omit some details of data

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Continuous variables

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- could have an infinite number of values along a continuum - Coding procedures applied to display the data in categories

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Line Graphs

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- helps detect trends in the data - Single point= frequency of cases for each category of a variable - use of >2 lines = demonstrates comparisons among subgroups

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Pie Charts

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- Circle that show proportion of cases according to categories - Size of pie = proportional to the frequency of cases shows the relative importance of each subcategory

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Ratio

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- defined as "The value obtained by dividing one quantity by another." - Examples are: Rates, proportions and percentages expressed as x/y

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Proportion

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- a type of ratio in which the numerator is part of the denominator - the formula is (A/A+B)

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Percentage

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- A proportion that has been multiplied by 100 - The formula is (A/A+B) x 100

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Types of Epidemiologic measures

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- Quantitative terms are useful in epidemiology to characterize the occurrence of disease, morbidity, and mortality in population - Quantitative terms include: Counts, incidence, prevalence

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Rate

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- a type of ratio - differs from a proportion because the denominator involves a measure of time

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Count

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- refers to the number of cases of a disease or other health phenomenon being studied - reports of single cases may have public health significance

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General info regarding epidemiologic measures

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- epidemiologic measures provides the frequency of a disease or condition (ex,prevalence) - Association between exposures and health outcomes (ex, risk ratio) - strength of the relationship between an exposure and a health outcome (ex, risk ratio = 5.0)

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Incidence

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- Occurrence of new disease or mortality within a defined period of observation (ex, a week, month, year or other time period) in a specified population - expressed as a number

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Incidence rate

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- describes the probability of someone in that population developing the disease during a specified period conditional on not dying first from another disease - A rate formed by dividing the number of new cases that occur during a time period by the number of individuals in the population at risk - Incidence rate is a rate because of the specification of time in the denominator - Explains how fast the disease of occurring Formula: # of new cases during a time period/total population during the same time period X 100,000

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Population at risk

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- The members of the disease who are capable of developing the disease or condition being studied

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Prevalence

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- The number of existing cases (including new cases) of a disease or health condition, or deaths in a population at some designated time - Variations: Point prevalence period prevalence lifetime prevalence

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Point prevalence

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- all cases of a disease, health condition, or deaths that exist at a particular point in time relative to a specific population from which the cases are derived - Formula: (# of ill persons/ total # in the group) at a point in time

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Lifetime prevalence

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- Cases diagnosed at any time during the person's lifetime

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Period prevalence

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- a cases of a disease within a period of time - Formula: (# of ill persons/ total number in the group) over a period of time

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Interrelationships between Incidence and Prevalence

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- When incidence of a disease increases, prevalence of the disease also increases - Prevalence = incidence x duration

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Factors that increase prevalence

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- increase in incidence - longer duration of the case/disease - in migration of cases - prolongation of life of patients without a cure

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Epidemiologic measures related to morbidity and mortality

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Four measures of morbidity (illness) and mortality (death) are: crude rates, case fatality rates, proportional mortality ratio, cause specific rates

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Factors that decrease prevalence

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- decrease in incidence - shorter duration of disease - in migration of healthy people - improved cure rate of disease

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Crude Rate

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- Does not take into account the demographic makeup of the population that may affect the observed rate - summary rates based on the actual number of events (over a time period) - Formula: (# of deaths in a given year/ reference population) x 100,000

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Reference population

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- population from which cases of a disease have been taken

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Case Fatality rate

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- the number of deaths due to a disease that occur among persons who are affiliated with that disease - the numerator and denominator refer to the same time period - Formula: (# of deaths due to disease/#number of cases of disease) x 100

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Proportional mortality ratio

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- number of deaths within a population due to a specific disease or cause divided by the total number of deaths in the population - Formula: (mortality due to a specific cause during a time period / mortality due to all causes during the same time period) x 100

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Age specific rate

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- number of cases of disease per age group of the population during a specified time period - helps to compare causes of morbidity or mortality across age groups - Formula: (# of deaths among specific age groups/ # of persons who are in that specific group) x 100,000

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Sex specific rate

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- Formula: ( frequency of a disease in a gender group/ total # of persons within that gender group during a time period ) x 100,000

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Adjusted rates

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- A rate of morbidity or mortality in a population in which statistical procedures have been applied to permit fair comparisons across populations by removing the effect of differences in the composition of various populations. - age is a factor used in rate adjustment

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Online sources for retrieving epidemiologic information

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Google, CDC, Medline National Library of Medicine, National Institution of Health, American Public Health Association, Society for Epidemiologic Research, World Health Organization

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Factors that affect the quality of epidemiologic data

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- quality is determined by the sources used to obtain the data and how completely the data cover the reference population - the quality of data affects the permissible application of the data and the types of statistical analyses that may be performed

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1. What is the nature of the data, including sources and content?

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Vital statistics (birth, deaths), surveillance data, specialized surveys

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2. How available are the data?

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- Release of personally identifiable info is prohibited in the U.S. and many other countries - The HIPPA protects personal info contained in health records - individuals medical records that disclose patients identity, reveal his/her diagnosis and treatments, source of payment are confidential - Data banks that collect info from surveys may release de-identified epidemiologic data

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3. How complete is the population coverage?

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- The completeness of the population coverage affects the representatives of the data - Representativeness: generalizability of the finding to the population from which the data is collected from - Mortality statistics: good coverage of the population; Medical health records: may exclude some variables of interests

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4. What are the appropriate and inappropriate uses of the data?

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What kind of study design are you conducting? (cross-sectional, cohort, case-control)

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U.S.Bureau of the Census

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- Provides data that can be used to define the denominator in rates with respect to official estimates of total population size and subdivisions of the population by geographical area - Census is conducted every ten years

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Vital events

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deaths, births, marriages, divorces and fetal deaths

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Vital Registration system

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- the vital registration system in the US collects info routinely on these events - Legal authority for registration of vital events in the US: individual states, five US territories (ex, Puerto Rico), the Commonwealth of Northern Mariana islands, NY City, and Washington D.C. - Keeps records of vital events provides certification of marriage, divorce, birth and deaths

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Deaths

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- Mortality data are almost totally complete-deaths are unlikely to go unnoticed in the U.S. 1. Funeral director completes the death certificate (most common) 2. Attending physician completes the section on date and cause of death 3. If death occurred as a result of accident, suicide or homicide (in the absence of physician): medical examiner or coroner completes and signs the death certificate 4. State registrar checks for completeness and accuracy and send a copy to National Center for Health Statistics (NCHS) 5. NCHS compiles and publishes national mortality rates

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Death certificates

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Includes: 1. Demographic characteristics (age, sex, race) 2. Date and place of death (hospital, home, road) 3. Cause of death (immediate cause underlying cause, and contributing factors

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Issues with Death certificates

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1. Underlying cause of death sometimes is unclear 2. Diagnostic criteria may lack consistent standards 3. Some conditions may be unreported because of stigma

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Birth Statistics

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- includes live births and fetal deaths - presumed to be nearly complete - uses of birth certificates: calculate birth rates, helpful in understanding condition affecting neonate, birth defects, length of gestation, birth weight and demographic background of the mother - use of fetal death certificates: calculate fetal death rates

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Issues with Birth certificates

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- affected by mother's failure to recall events during pregnancy - may miss conditions (malformation, illnesses) that were not detected at birth

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Issues with Fetal death certificates

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- variations in state-state requirements for fetal deaths may hinder the utility of epidemiological studies (in addition to some of the problems we have identified before)

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Uses of Birth and Fetal death data in Epidemiologic research

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- studies of environmental influences upon congenital malformations - search for clusters of birth defects in areas where mothers could have been exposed to teratogen (agents that cause fetal malformations), such as pesticides and pollutants

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Three examples of surveillance programs

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communicable and infectious diseases, non-infectious diseases, risk factors for chronic diseases

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Public Health Surveillance

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- refers to the systematic and continuous gathering of info about the occurrence of diseases and other health phenomena - personnel analyze and interpret the data, distribute the data and associate findings to planners, health workers, and members of the community

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Syndromic Surveillance

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- Syndromes= collection of symptoms - monitoring the frequency of illnesses with a specific set of clinical features...gathers info about patients' symptoms (ex, cough, fever, or shortness of breath) during the early phases of illness Advantage: Mobilize rapid response, helps to determine outbreaks early, helps to determine outbreaks

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Simplified Version of steps in surveillance system

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occurrence of health-related event-> health-related recognized by reporting source-> health-related event reported to responsible public health agency-> control and prevention activities -> Feedback to stake holders

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Reportable and Notifiable Disease Statistics

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- reported and notifiable diseases: usually infectious and communicable diseases that might endanger a population - by legal statute, physicians and other health-care providers must report cases of certain diseases, known as reportable and notifiable diseases to health authorities

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Deficiency of reportable and notifiable data for epidemiological purposes

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- Population coverage may be incomplete - People may not seek medical attention (asymtomatic, and subclinical illness) - Physicians/providers may fail to fill out the proper forms - Physicians may be unwilling to risk the physicians-patient relationship - Less serious conditions are underreported (sore throat)

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Chronic Disease Surveillance: the example of asthma

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- Asthma, a highly prevalent disease that incurs substantial medical and economic costs, is associated with inflammatory lung and airway conditions - Asthma surveillance programs provide data necessary for the development and evaluation of healthcare services for afflicted persons - created in 1999 - helps people with asthma in the U.S. to better understand the disease and control symptoms

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Behavioral Risk Factor Surveillance System (BRFSS)

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- established in 1984 by CDC - all 50 states and other US territories use this system - monitors behavioral risk factors that are associated with chronic diseases - examples of data collected relate to: health risk behaviors, preventive health practices, and health care access

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Registry

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a centralized database for collection of information about a disease

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Register

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- refers to the document used to collect the information - Exs: the National Program of Cancer Registries, the Surveillance, Epidemiology, and End Results (SEER) program

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Purpose of Registries Example: National Program of Cancer Registries

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1. Monitor trends of various cancers over time 2. Determine patterns/distributions of cancer 3. Guide planning and evaluating of programs 4. Aid in setting priorities for health resource allocation 5. Aid with clinical, epidemiological, and health services research 6. Provide information on prevalence and incidence of cancer

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Data from the National Center for Health Statistics (NCHS)

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- Scope of information is extensive - Exs of surveys and data collection systems: The National Health Interview Survey (NHS), National Health and Nutrition Examination Survey (NHANES), National Health Care Survey, The Vital Statistics System

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Why do we need to collect data?

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- To show distribution of diseases - Allocation of resources (which lowers the morbidity and mortality rate)

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Life expectancy

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number of years that a person is expected to live, at any particular year

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Life expectancy at birth

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indicates the number of years a newborn infant would live if prevailing patterns of mortality at the time of its birth were to stay the same through his/her life

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Maternal Mortality

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- Encompasses maternal deaths that result from causes associated with pregnancy - A measure is the maternal mortality rate - Formula: (# of deaths assigned to causes related for childbirth/number of live births) x 100,000

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Infant mortality rate

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- number of infant deaths among infants aged 0-365 days during a year divided by the number of live births duringg the same year (expressed as rate per 1,000 live births) - related to inadequate health care and poor environmental conditions - Substantial racial and ethnic variations - Formula: (# of infant deaths among infants aged 0-365 days during the year/# of live births during the year) x 1,000

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Fetal Mortality

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- Death of the fetus when it is in the uterus and before it has been delivered - Two measures are: Fetal death rate, Late fetal death rate - fetal death rate formula: (# of fetal deaths after 20 weeks or more gestation/# of live births and number of fetal deaths after 20 weeks or more gestation) x 1,000 - Late fetal death rate formula: (# of fetal deaths after 28 weeks or more gestation/# of live births and number of fetal deaths after 28 weeks or more gestation) x 1,000

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Crude Birth Rate

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- Number of live births during a specified period such as a year per the resident population during the midpoint of the year - Affects the size of the population - Formula:(# of live births within a given period/population size at the middle of that period) x 1,000

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General Fertility Rate

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- Number of live births reported in an area during a given time interval divided by number of women aged 15-44 years in the area - Expressed as rate per 1,000 women aged 15-44 years Formula: (# of live births within a year/ # of women aged 15-44 years at midpoint of the year) x 1,000

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