introduction to epidemiology

Introduction to

EpidemiologySupervised by : Prof. Farouq Shakatreh Presented by :Aya kabar Suha Abdullah Tajdeeda Awad

Outlines

History of Epidemiology. Definition of Epidemiology and its components. Epidemiological Basic concepts. Aims of Epidemiology. Ten Uses of Epidemiology. Scope or The Areas of Application . Types of Epidemiological Studies.

Epidemiology

The term epidemiology derived from Greek words :

Epi

Demos

Logos

Among

People

Study

History of epidemiology

The history of epidemiology has its origin in the idea goes back to (400 B.C)

Hippocrates Who suggest that environment & human behaviors affects health.

History of epidemiology cont.

1662 – John Graunt, who published a landmark analysis of Mortality data.

It was the first quantify patterns of birth, death, and disease occurrence.


1800 – William Farr work by systematically collecting and analyzing Britain's mortality statistics.

Farr, considered the father of modern vital statistics and surveillance, developed many of the basic practices used today in vital statistics and disease classification.


1854 -John Snow , was considered the “father of field epidemiology.

John Snow was conducting a series of investigations.

Twenty years before the development of the microscope, Snow conducted studies of cholera outbreaks both to discover the cause of disease and to prevent its recurrence.


19th and 20th centuries epidemiological methods applied in investigation of disease occurrence , at that time, most investigators focused on acute infectious diseases.

1930s &1940s non-infectious diseases were also investigated for their risk-factors, (as lung cancer to smoking)


1980s -extended to the studies of injuries and violence.

Beginning in the 1990s after the terrorist attacks of September 11-2001, epidemiologists have had to consider not only natural transmission of infectious organisms but also deliberate spread through biologic warfare and bioterrorism

Definition of Epidemiology

according to WHO

Is a study of distribution & determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

Components of the definition

Components of the definition

Is a study of

distribution & determinants of health-related

states or events in specified populations, and

the application of this study to the control of

health problems.

1 2 3

4 5

6

Components of the definition cont.

Study:Systematic collection, analysis and interpretation of data.Including : observation ,hypothesis testing , analytical research and experiments.

1


Distribution : Refer to analysis of an event by person, place

& time Epidemiology studies distribution of diseases

it answers the question: who, where and when?

Who? Where? When?

2


Epidemiology is concerned with the frequency and pattern of health events in a population.

A. Frequency:refers not only to the number of cases, but also to the relationship between the number of cases and the size of the population

2


B. Pattern:

Refers to the occurrence of health-related events by time, place, and person.

o Time patterns may be annual, seasonal, weekly, daily.

o Place patterns include geographic variation, urban/rural differences, and location of work sites or schools.

o Personal characteristics such as age, sex, marital status, and socioeconomic status, as well as behaviors and environmental exposures.


Determinant: It is any factor that influence health as : chemical , physical, social , biological , economic , genetic, behavior.

Epidemiology is also used to search for determinants, which are the causes and other factors that influence the occurrence of disease and other health-related events.

3


To search for these determinants, epidemiologists use analytic epidemiology or epidemiologic studies to provide the “Why?” and “How?” of such events.

?Why?

HOW?


Health-related state or event : It is defined as anything that affects the well-being of a population.As : disease, cause of death, behaviors ,ect…

4


Specified populations : Although epidemiologists and direct health-care providers (clinicians) are both concerned with occurrence and control of disease, they differ greatly in how they view “the patient.”

The clinician is concerned about the health of an individual.

The epidemiologist is concerned about the collective health of the people in a community or population.

5


Application of this study to the control:

Epidemiological studies have direct and practical applications for prevention of diseases & promotion of health Epidemiology is a science and practice Epidemiology is an applied science

6

Epidemiology is concerned with:

Distribution and determinants of health and diseases Morbidity Mortality Disability

Morbidity & Mortality

Morbidity: refers to the state of being diseased or unhealthy within a population.

Mortality : refers to the number of people who died within a population.

Morbidity

It is the Incidence of disease , it may cause

Death not cause death

By another meaning : mortality refers to the state of being diseased or unhealthy within a population

Note :High morbidity rate means (vary common disease) as a diabetes , hypertension .

Mortality

It is the measurement of death .As HIV , Ebola virus disease .

Note : High mortality rate means more incidence of death.

Example

mortality & morbidity


That means disease is vary common and incidence of death is vary high.

That means disease is un common and incidence of death is low.

As: acute pencrititis As : vitiligo

Example



That means disease is vary common and incidence of death is vary low .

That means disease is un common and incidence of death is high .

As : Diabetes As: Amyotrophic lateral sclerosis (ALS)

Basic concept

Risk: The probability of having a bad outcome.

Risk factors : A condition , physical characteristic or behavior that increases the probability that a currently healthy individual will develop a particular disease. “ p value ≤ 0.05 “

Basic concept cont.

Modifiable risk factors:

A risk factor that can be reduced or controlled by intervention, thereby reducing the probability of disease. As : (Physical inactivity , Tobacco use ,Alcohol use , Unhealthy diets) .

Non-modifiable risk factors:

A risk factor that cannot be reduced or controlled by intervention, for example: Age , Gender , Race , Family history (genetics).

Basic concept cont.

Causality: A cause effect relationship.In epidemiology, the cause is the exposure and the effect is disease or death( criteria of causation )

Criteria of causation:

1- Temporality: the risk factor come before the disease. 2- Consisting: the result of the study should be comparable to the results of other studies.

3- Dose response: when the risk factor increase the disease should increase also vise versa.

4- Study design.

5- Degree of association.

Aims of Epidemiology

Epidemiology has three main aims:

1. To describe disease patterns in human populations.

2. To identify the causes of diseases (also known as etiology).

3. To provide data essential for the management, evaluation and planning of services for the prevention, control and treatment of disease.

ten Uses of Epidemiology

Because most uses of epidemiology need not be restricted to human populations, the expression "a host" is preferred to "the host" .

In addition, the term "disease" includes injury and it may involve a consideration of sequelae such as disability, defect and impairment.

ten Uses of Epidemiology cont.

1) To determine which in the three possible sets of disease factors, host, agent and environment, are important in the occurrence of a specific disease or class of diseases, and to explore the manner in which they interact.

Epidemiological Triangle


Agent, or microbe that causes the disease (the “what” of the Triangle)

Host, or organism harboring the disease (the “who” of the Triangle)

Environment, or those external factors that cause or allow disease transmission (the “where” of the Triangle)

TB

Agent TB organism

EnvironmentCrowding Poor ventilationBad sanitation

HostPoor nutritionConcurrent diseaseLow immunity


2) To study the occurrence of disease in a population for purposes of community diagnosis and prognosis.

A clinician sees a disease as it occurs in an individual.

The epidemiologist is interested in the individual too, but his attention is primarily directed toward the group.


The severity of disease in a community can be gauged by several indices:

whether it is a leading cause of death; whether it has a high case fatality or other measure of

complications; whether it involves a large proportion of the young; whether it leaves permanent disability, defect or

impairment; whether it adversely affects the economic status of a

community.

The role of the epidemiologist can be described as that of a community diagnostician.


3) To describe the epidemiology of a disease or class of diseases.

Facts or events relating to the occurrence of a disease (or class of diseases) constitute its epidemiology.

The occurrence of a disease and its severity and outcome are resultants of a complex of interacting factors, some of which are host factors and others, agent and/or environmental.


A description of the epidemiology of a disease involves a thorough study of that disease in all its aspects including its frequency in various population, and known and suggested factors in the premorbid, morbid and post-morbid periods.

The premorbid period is the period preceding the inception of a disorder.

The morbid period, the pathological and clinical course .

The post-morbid period, the aftermath.


4) To measure risk. The epidemiologist may use rates which can show the

probability that could make : A person acquire a particular disease during a given period of

time (attack rate, morbidity rate, case incidence rate). A person have a particular disease at a given point in time

(prevalence rate). A person die of a particular disease during a given period of

time (mortality rate, death rate); or if he has a particular disease, that he will die of it during a given period of time (case fatality rate).

Such probabilities are measures of risk and they are useful to know prognosis.


5) To study the occurrence of disease or death with time as a variable. Such a study is referred to as a historical study.

In historical studies, it often is convenient to speak of trends, namely, secular trends and cyclic trends.

A secular trend ranges over a long period such as a century, and portions of it may increase, decrease or remain stationary. A cyclic trend must exhibit periodic fluctuations regardless of its duration either long or short


6) To aid in the search for causes of disease.

In general, a cause can be defined as an agent or any host or environmental factor that is influential in producing disease or accelerating its appearance.


7) In disease prevention and control. The epidemiologist helps to control a disease

when he identifies it, describes its epidemiology, demonstrates its existence in a community and investigates its source.

Primary control or disease prevention is the ideal control measure, it aims to Prevent the initial development of the disease.

Secondary control consists of diagnosis and treatment, it aims to reduce the severity and prevent complications.

Tertiary control involves rehabilitation of the disabled and correction of defect or impairment.


8) To aid in the identification of clinical syndromes.

A syndrome is a group of signs and symptoms that occur together and characterize a disease.


9) To aid in the detection of pre-symptomatic and latent disease.

Many diseases such as tuberculosis, diabetes, hypertension, g cancer of the cervix, neoplasms of the lung can be detected before the onset of symptoms or the development of serious changes.

The way to accomplish this is through mass screening

techniques , pre-employment physical examinations, periodic health examinations, special surveys and routine examinations in hospitals and clinics.


10) In administrative medicine and operations research.

One might evaluate the success of a disease control program; the needs of a hospital in terms of equipment, personnel and space; the quality of medical care in a community; and the efficiency of hospital administration

Scope of Epidemiology

Strictly Speaking, There Is No Life Science, Where Epidemiological Approach And Principles Cannot Be Applied.

From Womb To Tomb Epidemiology Is Applicable

Scope of Epidemiology cont.

Infectious disease epidemiology

Occupational Injury Cardiovascular disease

epidemiology Cancer epidemiology Epidemiology of Aging Obesity/

diabetes epidemiology

By physiology/disease:

Environmental epidemiology

Economic epidemiology Clinical epidemiology Genetic epidemiology Nutritional epidemiology Conflict epidemiology Social epidemiology Primary care

epidemiology

By methodological approach:

Some of application areas

Types of epidemiological Studies

Study design: is defined to be the process of planning an empirical investigation to assess a conceptual hypothesis about the relationship between one or more exposure and a health out come

Types of epidemiological Studies cont.

1. Observational studies: Descriptive study : ( cross sectional ) Analytic study : (cohort , case

control)

2. Experimental studies: • Community trails • Clinical trails

Study design

ExperimentalObservation

( comparison group)

Randomized Clinical trial”“ Community trial

Non-randomizedAnalytical

NO YESDescriptive

Cross-sectional

Cohort Case – control

Descriptive study(Cross –sectional study)

Cross-sectional is : the collection of data from more than one case at one moment in time.

(Examines relationship between exposure and outcome prevalence in a defined population at a single point in time).

In cross sectional studies individuals are classified as diseased and disease free and exposed and not exposed to the risk factor at single point of time.

(Cross –sectional study) cont.

It helps to know: 1.Prevalence rate 2.Risk factor

It is The basics for further studies.

It provides association not causation.


Advantages:*Less time-consuming than case-control or cohort studies.*Inexpensive.*Good, quick picture of prevalence of exposure and prevalence of outcome.

Disadvantages:*Difficult to determine temporal relationship between exposure and outcome (lacks time element).*Not suitable for rare disease.*Unable to measure incidence.

Analytical Studies

A method for testing a hypothesis as part of an investigation of the association between a disease and possible causes of that disease) .

They describe association between exposure and outcome.

Risk factor Disease

Cohort studies

A cohort study typically examines multiple health effects of an exposure; subjects are defined according to their exposure levels and followed over time for outcome occurrence .

The rates of disease incidence among the exposed and unexposed groups are determined and compared.

Measure of association “ relative risk”.

Cohort studies cont.

Present

Future


1.Prospective cohort :

outcome occurs after the study is initiated.

Time consuming, expensive

More valid information on exposure.

Inefficient for rare diseases


2.Retrospective cohort study: Outcome has already occurred at study

initiation (cohort of exposed & unexposed are assembled from past medical records and followed forward to determine present incidence of disease).

Cheaper and faster than a prospective study Requires good historical exposure data on

subjects(accurate records). Looks back in time to study events that

have already occurred .

Retrospective cohort study

Measure exposure

and confoundervariables

Exposed

Non-exposed

Outcome

Outcome

TimeStudy begins here

Cohort studies cont.Advantages: Can evaluate multiple effects of a single exposure More efficient for rare exposures and outcomes with long

induction and latency periods Can directly measure incidence Clear chronological relationship between exposure and

outcomeDisadvantages:

• Expensive

• Time-consuming

• Inefficient for rare diseases with long latency.

• Loss to follow-up

Case-Control Studies

Examines multiple exposures in relation to an outcome; subjects are defined as cases and controls, and exposure histories are compared.

First, identify the cases and the controls. Then, look back in time to learn which subjects in each group had the exposure(s).

Efficient for rare diseases.

Measure of association “odds ratio “.

Case-Control Studies cont.

Exposure present

Exposure absent

Exposure present

Exposure absent

Cases(disease present)

Controls( disease absent)

Studypopulation

TIMEPAST PRESENT

Study begins here

Case-Control Studies cont.

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 subjects’ memory and reports).*Inefficient for rare exposures (such as*Difficult to establish clear chronology of exposure and outcome).

Cohort

Case - control

Yes

Rare disease

Yes

Rare exposure

Yes

Multiple outcome

Yes

Several risk factors

Yes

Dose – response relations

Yes

Disease with long latent period

Experimental Studies

Two types:

1- Controlled clinical trials (Randomized

Control Trials) Emphasis on the individual

2- Community interventionsEmphasis on the community

Experimental Studies cont.

There are three key components of an experimental study design:

(1) pre-post test design . (2) a treatment group and a control group . (3) random assignment of study participants.

Randomization:◦ Equal probability of participants to be

assigned to intervention or control groups


Randomization

Studypopulation

Intervention

Control

Outcome

Not outcome

Outcome

Not outcome

Time

Study begins here (baseline point)

Future


Advantages:*Best evidence study design.*No inclusion bias. *Controlling for possible confounders.*Comparable groups (using randomization).

Disadvantages:*Large trials.*Long term follow-up (possible losses).*Expensive.*Possible ethical questions.

CONFOUNDING

Confounder: a factor that distorts the true relationship of the study variables because of being related to both the outcome and the exposure.

Distorted estimating of exposure effect results because the exposure effect is mixed with the effect of extraneous variable .

Also called third variable

CONFOUNDING cont.

Exposure

Outcome

Confounding

variable

Association

Associations of a hypothetical exposure, disease, and confounding variable

Association Association

CONFOUNDING cont.

Smoking Cancer

Pollution

Association

Association Association

Associations of smoking, cancer, and pollution

CONFOUNDING cont.

To be a confounding factor, two conditions must be met:-

1- Be associated with exposure without being a result of exposure.

2- Be associated with outcome independently of exposure (not an intermediary).

CONFOUNDING cont.

Confounding can be controlled by:

- Randomization: assures equal distribution of confounders between study and control groups.

- Restriction: subjects are restricted by the levels of a known confounder.

- Matching: potential confounding factors are kept equal between the study groups.

- Stratification for various levels of potential confounders.

Thank you !

introduction to epidemiology

Science

definition of epidemiology

term epidemiology

uses of epidemiology

father of field epidemiology

pattern of health events

control of health problems

john snow

studies of injuries