Community Health : Chapter 10 : Epidemiological Applications

Introduction

• The public health science of epidemiology has made major contributions to.

  • Understanding the factors that contribute to health and disease.

  • The development of health promotion and disease-prevention measures

  • The detection and characterization of emerging infectious agents

  • The evaluation of health services and policies

  • The practice of nursing in public health

Epidemiology

The study of the distribution and factors that determine health related states and/or events in a population ; we use this information to control health problems

Distribution

Patterns of health events in populations

outcome

In order to understand the _______ we need to understand the what, who, when, where, why, and how

Outcome

_______ is who was affected, where are they, when did these events occur

Descriptive Epidemiology

Form of epidemiology that describes a disease according to its person, place, or time

For example : What is the disease? Who is affected? Where are they? When do events occur?

Analytic Epidemiology

• Looks at ideology or origins of a disease ; deals with determinants of health and disease (the how and the why)

  • Determinants of health event

  • For example : How does it occur? Why are some people affected more than others?

How and Why

• Factors such as exposure characteristics, behaviors, and contexts that determine and influence the pattern

Descriptive Epidemiology Question Words

• What

• Who

• Where

• When

Analytic Epidemiology Question Words

• How

• Why

Purpose of Epidemiology

• The study of populations to

  • Monitor the health of the population

  • Understand the determinants of health and disease in communities

  • Investigate and evaluate interventions to prevent disease and maintain health

4th Century BCE : Hippocrates

• First person to use ideas that are now what we know for epidemiology today

18th and 19th Century

• Comparison groups began to be used and measure change or the effect of some actions or treatment on an experimental group

• John Snow - Father of epidemiology

• Florence Nightingale

John Snow ; Water pump and cholera outbreak map

Who is the father of Epidemiology? What did he do?

Florence Nightingale

• Outbreaks during Crimean war

• Handwashing efforts

20th Century

• Shifted from looking for single agent (1 cause) to determining that there are multiple factors in development of these outbreaks

• Started looking at genetics and molecular techniques

• HIV, AIDS, SARS, COVID

• Bioterrorism and preparing public

New Nurses Use Epidemiology

o   Nurses look at health and at disease causation, and how both prevent and treat illness.

o   Nurses are involved in the surveillance and monitoring of disease trends, for example, homes, schools, workplaces, and clinics.

o   Provides baseline information for assessing needs of clients, identifying specific problems, designing appropriate strategies to evaluate the problems, set priorities, develop a plan of care, and evaluate effectiveness

causation

Nurses now look at health and disease ________, and how both prevent and treat illness

Healthy People 2030

• Examples of Epidemiologic Objectives in Healthy People 2030

  •  D-09: Reduce the rate of death in adults with diabetes.

  •  FS-07: Increase the proportion of people who wash their hands and surfaces often when preparing food.

  • DS-10: Increase the proportion of people who refrigerate food within 2 h after cooking.

D-09

• Reduce the rate of death in adults with diabetes.

FS-07

• Increase the proportion of people who wash their hands and surfaces often when preparing food.

DS-10

Increase the proportion of people who refrigerate food within 2 h after cooking.

Proportions

• Ratio in which the numerator includes the denominator

• Our definition - type of ratio that relates to a whole part

• Ex ; a class with 20 men and 80 women have a total class size of 100 people

  • Proportion of men is 20 men : 100 people

Rates

• Measures frequency of health event of different populations at certain times

• Special type of ratio that incorporates the dimension of time in the denominator

• Ex ; 50 MPH

denominator ; numerator

A rate is not the same as a proportion because the ________ is a function of population size and dimension of time whereas the ________ is the number of events

Risk

• Probability of risk is a population of persons for whom there is some finite probability of that event occurring (even if it is small)

risk

In Epidemiology, they use the term ______ to mean the probability of an outcome (normally negative) in a specified period of time

quantifiable

Risk usually applies ________ numbers or concepts such as the risk of dying, the risk of having a heart attack

Measures of Incidence

• Measure of how common or frequently a disease occurs in a specified population over a period of time by providing a quick measurement of new disease diagnosis

• Ex ; the risk of developing diabetes in 21 year old college students who eat a high fat high simple carbohydrate diet by the time they are 40

Prevalence Proportion

• Proportion of a population with a specific characteristic in a specific time period

  • Ex ; 60 people have pressures ulcers out of 240 patients in the hospital

  • That is 25% of the population in the hospital with pressure ulcers

  • 60 divided by 240 = .25

Attack Rate

• Proportions of persons exposed to an agent and developing a disease

  • Exposure to food-borne pathogens

    • % of people who at the chicken and got sick

Mortality Rates

• Are not true rates but proportions

• Reflects serious health problems and changing diseases

  • How many people died of heart disease

• Infant mortality rate as indicator community health

Endemic

Condition when the number of conditions present are expected

Outbreak

Condition that occurs in excess of what would be expected in an endemic level

• Increased rate of measles

Epidemic

Occurs when a disease injuring exceeds the unusual level of the condition and spreads over a large area

Pandemic

• Epidemic that spreads globally

• COVID19, Spanish Influenza of 1918 - affected 1/3 of the population, and SARS in 2003

Spanish Influenza

• 1918

• Affected over 1/3 of the population

SARS

• 2003

Herd Immunity

Resistance of a group of people to an attack by a disease to which a large portion of the population is immune

• A goal we having in community health

Epidemiologic Triangle Components

• Agent

• Host

• Environment

triangle

Changes in any part of the _______ can influence the occurrence of a disease by increasing or decreasing a person’s risk for the disease

Agent

An animate or inanimate factor that must be present or lacking for a disease or condition to develop

Host

A living species (human or animal) capable of being infected or affected by an agent

Environment

All that is internal or external to a given host or agent and that is influenced and influences the host and / or agent

Web of Causality

• Associations are sometimes mutual, with lines of causality going in both directions

• Spider-web

• Complex interrelationship and subtle ways we can increase or decrease the risk of the disease

Ecological Model

• Bridge between descriptive and analytic epidemiology

• Looking at multiple factors in ideology and how those factors come together to cause disease

descriptive, analytic

Ecological Model is the bridge between _______ and ________ epidemiology

Levels of Preventive Interventions

• Primary

• Secondary

• Tertiary

Primary

• Intervention to seek to prevent health and reoccurrence of disease or injury

  • Vaccines

Secondary

• Seek to detect disease early in its progression before you have clinical signs or symptoms that are obvious

  • Mammograms

Tertiary

• Aimed to limit disability Rehabilitation of disease or injury

Preventive Intervention Levels Summary

• Primary - prevent*

• Secondary - seek to detect disease early in progression

• Tertiary - aimed to limit disability

Surveillance

Involves systematic collection, analysis, and interpretation of data related to the current of the disease and the health status of a given population

Passive Surveillance

• More COMMON in local and state health departments

• Health care providers in the community report cases of notifiable disease to public health authorities through the use of standardized reports

• Relatively inexpensive but very limited due by variability and incompleteness in provider reporting practices

  • STD

Active Surveillance

• Purposeful, ongoing search for new cases of disease by public health personnel, through personal or telephone contacts or the view of laboratory reports or hospital or clinic records

• Costly

  • Often limited to brief periods of specific purposes as in the emergence of an newly identified disease, a particularly severe disease, or the reemergence of a previously eradicated disease

    • COVID-19 Pandemic

Screening

• Reliability

• Validity

Reliability

• Precision of the measurement

• Consistency or repeatability of the measurement

• 3 sources of error

  • 1. Variation inherent in the trait being measured (e.g, blood pressure changes with time of day, activity, level of stress)

  • 2. Observer variation, which can be divided into intraobserver reliability (i.e., consistency by the same observer) and interobserver reliability (i.e., level of consistency from one observer to another)

  • 3. Inconsistency in the instrument, which includes the level of internal consistency of the instrument (e.g., whether all items in a questionnaire measure the same thing) and the stability (i.e., for test-retest reliability) of the instrument over time

Reliability - 3 Sources of Error

• 1. Variation inherent in the trait being measured (e.g, blood pressure changes with time of day, activity, level of stress)

• 2. Observer variation, which can be divided into intraobserver reliability (i.e., consistency by the same observer) and interobserver reliability (i.e., level of consistency from one observer to another)

• 3. Inconsistency in the instrument, which includes the level of internal consistency of the instrument (e.g., whether all items in a questionnaire measure the same thing) and the stability (i.e., for test-retest reliability) of the instrument over time

Validity

• Is the measurement really measuring what we think it is, and how exactly?

• Measured by sensitivity and specificity

sensitivity and specificity

What is validity measuring?

Sensitivity

Quantifies how accurately the test identifies those with the condition or trait

• Represents the proportion of persons with the disease whom the test correctly identifies as positive (true positive)

• High sensitivity

True Positivity

Represents the proportion of persons with the disease whom the test correctly identifies as positive (true positive)

High Sensitivity

Needed when early treatment is important and when identification of every case is important

Specificity

• Indicates how accurately the test identifies those without the condition or trait (i.e., the proportion of persons whom the test correctly identifies as negative for the disease (true negative)

True Negative

The proportion of persons whom the test correctly identifies as negative for the disease

High Specificity

Needed when rescreening is impractical and when it is impractical and when it is important to reduce false-positive results

Positive-Predictive Value

Proportion of persons with a positive test who actually have the disease, interpreted as the probability that an individual with a positive test has the disease

Negative-Predictive Value

Proportion of persons with a negative test who are actually disease-free

Sources of Data - 3 Main Types

• Routinely Collected Data

• Data collected for other purposes but useful for epidemiologic research

• Original data collected for specific epidemiological studies

Routinely Collected Data

• Secondary data

• Census data, vital records (birth certificates and death certificates), surveillance data (systematic collection of data concerning disease occurrence) as carried out by CDC

• Vital records are the PRIMARY source of birth and mortality statistics

Data Collected for Other Purposes

• Secondary data

• Medical, health department, and insurance records

Original data collected for specific epidemiologic studies

• Primary data

Rate Adjustment Types

• Age-adjusted rate

• Direct-adjusted rate

• Indirect-adjusted rate

Age-adjusted rate

• Can be performed by direct or indirect methods

• Both methods require a standard population, which can be an external population, such as the US population for a given year, a combined population of groups under study, or some other standard chosen for relevance or convenience

Direct-adjusted Rate

• Applies the age-specific death rates from the study population to the age distribution of the standard population

• The result is the (hypothetical) death rate of the study population if it had the same age distribution as the standard population

Indirect-adjusted rate

• Age-specific death rates of the standard population applied to the study population’s age distribution result in an index rate that is used with the crude rates of both the study and standard populations

• Hypothetical

• May be required when the age-specific death rates for the study population are unknown or unstable (e.g., based on relatively small numbers)

Standardized Mortality Ration (SMR)

The number of observed deaths in the study population divided by the number of deaths expected on the basis of age-specific rates in the standard population and the age distribution of the study population

Comparison Groups

• Used to decide if the rate of disease is the result of a suspected factor

• Comparing the exposed group to the group of comparable unexposed persons

Descriptive Epidemiology

Describes the distribution of disease, death, and other health outcomes in the population according to person, place, and time

• Provides a picture of how things are or have been and describes the who, where, and when of disease patterns

Analytic Epidemiology

• Looks for the determinants of the patterns observed - the how and why

• These concepts and methods are used to identify what factors, characteristics, exposures, or behaviors might account for differences in teh observed patterns of the disease occurrence

observational

Descriptive and Analytic studies are _________ ; in these studies the investigator observes events as they are or have been and does not intervene to change anything or to introduce a new factor

Descriptive Epidemiology Components

• Person

• Place

• Time

Person

• Race

• Sex

• Age

• Education

• Occupation

• Income

• Socioeconomic status

• Marital status

Age

_____ is the most important predictor of overall mortality

Mortality

The ________ curve by age drops sharply during and after the first year of life to a low point in childhood, then begins to increase through adolescence and young adulthood, and after that increases sharply through middle and older ages

sex, race

Mortality and Morbidity differ by ______ and _______

Place

• Examine geographic patterns

• Does the rate of disease differ from place to place (e.g., with local environment)?

• Geographic variations can be caused by :

  • Differences in the chemical, physical, or biological environment

  • Differences in population densities, customary patterns of behavior and lifestyle, or other personal characteristics

Time

• Third component of descriptive epidemiology

• Is there an increase or decrease in the frequency of disease over time? Are there temporal and spatial patterns evident?

Temporal Patterns

• Secular Trends

• Point Epidemic

• Cyclical Patterns

• Event-Related Clusters

Secular Trends

• Long-term patterns of morbidity or mortality rates (i.e., over years or decades)

• May reflect changes in social behavior or practices

  • Ex ; increased lung cancer mortality rates in recent years reflect a delayed effect of the increased smoking in prior years

  • Ex ; the decline in cervical cancer deaths is primarily the result of widespread screening with the Pap test

• Some secular trends may result from increased diagnostic ability or changes in survival (or case fatality) rather than in incidence

  • Ex ; case fatality from breast cancer has decreased in recent years, although the incidence of breast cancer has increased

Point Epidemic

• A time-and-space related pattern that is important in infectious disease investigations and as an indicator for toxic exposures

• Most clearly seen when the frequency of cases is graphed against time

• The sharp peak characteristic of such graphs indicates a concentration of cases over a short interval of time

• The peak often indicates the population’s response to a common source of infection or contamination to which they were all simultaneously exposed

• Knowledge of the incubation or latency period (time between exposure an development of signs and symptoms) for the specific disease entity can help to determine the probable time of exposure

• Ex ; an outbreak of gastrointestinal illness from a food-borne pathogen

Cyclical Time Patterns

• Seasonal fluctuation is a common type of cyclical variation in some infectious illnesses

  • Seasonal changes may be influenced by changes in the agent itself, changes in population densities or behaviors of animal reservoirs or vectors, or changes in human behaviors resulting in changing exposures (e.g., being outdoors in warmer weather and indoors in colder months)

Non-simultaneous, event-related clusters

• Patterns in which time is not measured from fixed dates on the calendar but from the point of some exposure, event, or experience presumably held in commonly affected persons, although not occurring at the same time

• Ex ; vaccine reactions during an immunization program

Analytic Epidemiology Goal

• To discover the determinants of outcomes - the how and why

Analytic

________ epidemiology deals with the factors that influence the observed patterns of health and disease and increase or decrease the risk of adverse outcomes

Types of Analytic Epidemiology

• Cohort Studies

  • Prospective Cohort Studies

  • Retrospective Cohort Studies

• Case-Control Studies

• Cross-Sectional Studies

• Ecological Studies

Cohort Studies

• The standard for observational epidemiologic studies

• Comes closest to the idea of a natural experiment

• Cohort - used in epidemiology to describe a group of persons who are born at about the same time

• Cohort refers to a group of persons generally sharing some characteristic of interest

Prospective Cohort Studies

• Longitudinal or follow-up study

• Subjects who do not have the outcome under investigation are classified on the basis of the exposure of interest at the beginning of the follow-up period

• The subjects are then followed for some period of time to determine the occurrence of disease in each group

  • The question is “Do persons with the factor (or exposure) of interest develop (or avoid) the outcome more frequently than those without the factor (or exposure)?”

beginning

In Prospective Studies care is classified on the exposure of interest at the _________ of the follow-up period

Retrospective Cohort Studies

• Combine some advantages and disadvantages of case-control studies and prospective cohort studies

• Rely on existing records, such as employment, insurance, or hospital records, to define a cohort that is classified as having been exposed or unexposed at some time in the past

• The cohort is followed over time using the records to determine if the outcome occurred

• May be conducted entirely using past records or may include current assessment or additional follow-up time after study initiation

  • This approach saves time, however its accuracy relies on existing historical records ; however, its accuracy relies on existing historical records