Epidemiology v1.5 unit 1

Basic Epidemiology
BPH 102.2 BE
Unit 1: Meaning, Type, Scope and Application of
Epidemiology (10 hours)
Draft Version 1.5 (feedback welcomed)
Upendra Raj Dhakal
Lecturer: Valley College of Technical Sciences
urdhakal@gmail.com
9849110689

Concept
• In Greek Word,
• Epi – on or upon/among
• Demos – People
• Logos – Study
• Word meaning says, Epidemiology is a study done upon people.
• Epidemiology is the basic science of Public Health.
Draft Version 1.5 (Feedback Welcomed)

Definition
• Epidemiology is the study of the distribution and determinants of
health related states or events in specified populations, and the
application of this study to the control of health problems (Last,
1988)
• The branch of medical science which treats epidemics (Oxford English
Dictionary)
• Epidemiology is the study of Epidemics and their prevention (Kuller
LH: American J of Epidemiology 1991; 134:1051)
• The study of occurrence of Illness (Anderson G. In: Rothman KJ:
Modern Epidemiology)

Historical Development of Epidemiology
• Hippocrates (460 – 377 BC): Malaria associated with swampy environment.
• John Graunt (1662): “Nature and Political Observations Made Upon the Bills of Mortality” – First
to employ quantative methods in describing population vital statistics.
• Edward Jenner in late 18th century: Cow pox protects from small pox; first vaccination.
• John Snow (1850): Formulated natural epidemiological experiment to test the hypothesis that
cholera was transmitted by contaminated water.
• Ignaz Semmelweis in 19th century: Childbed fever (puerperal sepsis)
• Florence Nightangale: Epidemic typhus during war of Crimean in mid 19th century.
• Doll & Hill (1950): Used a case control design to describe and test the association between
smoking and lung cancer.
• Frances et. al (1950): Huge formal field trial of the Poliomyelitis vaccine in school children.
• Dawber et. al (1955): Used the cohort design to study risk factors for cardiovascular disease in the
Framingham Heart Study.

John Snow and Cholera
• Cholera epidemics in London 1846 – 1849
• Snow analyzed the death records and interviewed
survivors
• Created map
• Most individuals who died of cholera used water
from Broad street pump
• Survivors did not drink water but beer instead or
used another pump
• Identified the Broad street water pump as likely
source
• After closing this pump number of cholera cases
dropped significantly

Florence Nightingale and Epidemic Typhus
• Recorded statistics on epidemic typhus in
English civilian and military populations
• Published a 1000 page report in 1858:
oStatistically linked disease and death
with poor food and unsanitary
conditions
oNovel graph: coxcomb chart or polar
area diagram chart
➢Fixed angle and variable radii
• Resulted in reforms in the British Army
• Nightingale became the first female
member of the Statistical Society

Aims of epidemiology
• To describe the health status of a population
• To access the pubic heath importance of disease
• To describe the natural history of disease
• To explain the etiology of disease
• To predict the disease occurrence
• To evaluate the prevention and control of disease
• To control the disease distribution
Descriptive epidemiology
Analytical epidemiology
Applied/Experimental/Int
erventional epidemiology

Scope of Epidemiology
• Disease definition: Characteristics or Combination of character that best
discriminate disease from non disease
• Disease occurrence: The rate of development of new case in population. The
proportion of current disease within population
• Disease causation: The risk factors for disease development and their relative
strength with respect to an individual and population
• Disease outcome: The outcome following disease onset and of the risk factors
• Disease management: The relative effectiveness of proposed therapeutic
interventions
• Disease prevention: The relative effectiveness of proposed preventive strategies
including screening
These Scope can be classified into Classical Epidemiology, Clinical Epidemiology
and Research which are eventually are applied

Purpose of Epidemiology
• To investigate nature/extent of health – related phenomena in the
community.
• To study natural history and prognosis of health – related problem.
• To identify causes and risk factors.
• To recommend/assist in application of/evaluate best interventions
(preventive and therapeutic measures)
• To provide foundation for public policy.

Branch of Epidemiology
• Molecular Epidemiology: Concerns with the application of molecular biology to
study various epidemic problems. It deals with DNA Cloning, Nucleic Acid
Analysis, Polymerase chain reaction, etc.
• Disaster Epidemiology: It helps to find mechanisms in order to reduce the
negative health effects of disaster. It generates information about the disaster
situation where it uses techniques like identification of potential diseases,
establishment of surveillance system, etc.
• Travel Epidemiology: It is concerned with health risk during travelling. Generally,
it deals with high altitude, snow blindness, heat exhaustion, dehydration,
frostbite, etc.
Epidemiology can also be branched as Environmental Epidemiology, Genetic
Epidemiology, Nutritional Epidemiology, Occupational Epidemiology, Injury
Epidemiology, Chronic Disease Epidemiology, Life Style Epidemiology, Social
Epidemiology, etc.

Types of Epidemiological Studies (Design)
Study
Observational
Analytical
Cross sectional
study
Longitudinal
Study
Case Control Study
Cohort Study (Retrospective and
prospective)
Descriptive
Case Study
Case Series Study
Cross – sectional Study
Ecological/Correlational
Study
Experimental
Randomized Control Trial (RCT)
Quasi Experimental
Community Trial
Field Trial
Populations
(Correlational studies),
and Individual
Study of
occurrence
and
distribution of
disease
Further studies
to determine the
validity of a
hypothesis
concerning the
occurrence of
disease
Deliberate
manipulation of the
cause is predictably
followed by an
alternation in the effect
not due to chance
It is applied or
interventional
type of study

Best Practice of software
Study Type Analysis Type Best suited statistical package
Cross – sectional Descreptive EPI Data
Analytical EPI Data, SPSS
Case Control Descreptive, Analytical SPSS, SAS, R, STATA
Cohort Descreptive, Analytical SPSS, STATA, R, SAS
RCT Descreptive, Analytical SPSS, STATA, SAS
Quasi Experimental Descreptive, Analytical SPSS, STATA, SAS

Use of Epidemiology
• To find the causation of the disease.
• To describe natural history of disease.
• Description of health status of population.
• Evaluation of intervention.
• Community diagnosis
• Planning and evaluation
• Investigate epidemics of unknown etiology
• Elucidate mechanism of disease transmission

Spectrum of Health and Disease
• It is a graphical representation of variation of disease manifestation,
which is similar to the spectrum of light. It is called spectrum, because
there is no clear cut demarcation between the health and disease
status and we cannot determine where one ends, and another
begins.
Optimum health
Better health
Normal health
Health & Disease Disease with undiagnosed
Disease with diagnosed
Severe disease
Death

Determinants of Health and Disease
Determinants
of Health
Income and
Social Status
Social
support and
network
Employment
and working
condition
Physical
environment
s
Education
Healthy
child
developmen
t
Biology and
genetic
endowment
Health
services
Personal
health
practices
and coping
skills

Mode of transmission of Disease
Routes Diseases
Food Borne and Waterborne Travelers' diarrhea, Cholera, Cryptosporidiosis, Giardiasis,
Hepatitis A and E, Listeriosis, Typhoid Fever
Air Borne TB, SARS, Mumps, diphtheria, measles
Vector Borne Malaria, Yellow Fever, Dengue, Japanese Encephalitis,
Chikungunya and TB borne encephalitis
Animal Borne Rabies, Brucellosis, Leptospirosis
Blood Borne Hepatitis B and C, HIV/AIDS and Malaria
Sexually Transmitted Hepatitis, HIV/AIDS and Syphilis
Soil Borne Anthrax, Ascariasis, Trichuris, Fungal Infections
Recreational Water Leptospira, Pseudomonas, Legionellosis, Schistosoma, CLM,
Giardia, Cryptosporidium, Tinea and Cutaneous papilloma
It can also be classified as: Direct (Direct Contact, Droplet spread) and Indirect (Airborne,
Vehicleborne and vectorborne – mechanical: dust or biological: mosquito) –see old note

MoT: Fecal – Oral route of transmission (5F)

Relationship between Epidemiology and
Public Health
• Public Health is collective actions to improve population health
• Epidemiology is used in several ways as a tools for improving public health
• Early studies in epidemiology were concerned with the cause (etiology) of
communicable disease, and such work continues to be essential since it can
lead to the identification of preventive methods.
• In this sense, epidemiology is a basic medical science with goal of
improving the health of populations
• Epidemiology is one of the essential discipline of PH which creates
evidence (generally through disease surveillance), and other disciplines can
be used in dialogue between stakeholders and intervention.

Natural History of Disease
Stage of
susceptibility
Stage of
sub – clinical disease
Stage of
clinical disease
Stage of recovery,
disability or death
Exposure
Pathologic
Changes
Onset of
symptoms
Usual time of Diagnosis
(Early Dx) (Late Dx)
Primary prevention aims to
reduce occurrence
Secondary prevention aims to
reduce severity
Tertiary prevention aims
to reduce disability and
mortality
Health
Promotion
Specific
protection
Early detection
and treatment
Disability limitation Rehabilitation
Positive
health
Levels of prevention

Prognosis of Disease
Prognosis
Survival
5 – year
survival
Observed
survival
Median
survival
Relative
survival
Death
Case –
fatality Rate

Contd …
• Five-year survival rate is a type of survival rate for estimating the prognosis of a
particular disease, normally calculated from the point of diagnosis.
• Observed survival is an estimate of the probability of surviving all causes of death for a
specified time interval calculated from the cohort of cases.
• Median survival is a statistic that refers to how long patients survive with a disease in
general or after a certain treatment. It is the time—expressed in months or years—when
half the patients are expected to be alive. It means that the chance of surviving beyond
that time is 50 percent.
• Relative survival is defined as the ratio of the proportion of observed survivors in a
cohort of patients to the proportion of expected survivors in a comparable set of disease
free individuals.
• Case fatality rate / case fatality risk / case fatality ratio / fatality rate is the proportion
of deaths within a designated population of "cases" over the course of the disease. A
CFR is conventionally expressed as a percentage and represents a measure of risk.

Epidemiological Classification of Disease: Idea
and Need for Classification
• Epidemiological classification of disease is based on frequency and
distribution as sporadic, endemic, epidemic, and pandemic.
• Standard measurement is necessary for morbidity, mortality and
other health indicators
• 4.7 billion people speak more than 7000 language, and standard
classification of disease makes same recording and reporting
throughout the world.
• Standards classification, makes disease understand and treat similarly
throughout the globe, simply by generalizing the code.

Principle for classification (ICD – 11)
• A key principle for ICD – 11 is to Simplify coding structure and electronic
tooling – which allows health care professionals to more easily and
completely record condition.
• Basic Principle for ICD - 11 is not release yet. It is releasing soon.
• Specific Goals for ICD – 11:
➢Formulate multipurpose and coherent classification.
➢Serve statistical continuity.
➢Serve as an international and multilingual reference standards for scientific
comparability and communication process.
➢Ensure that ICD – 11 will seamlessly function in an electronic health records
environment by liking ICD logically to underpinning terminologies, ontologies, and
ICD categories defined by “logical operational rules” on their associations and details.

International Statistical Classification of
Diseases and Related Health Problems (ICD)
• ICD concept was first found practiced in England in 16th century, where
every week – mortality by scurvy, leprosy, and plague was announced
• In late 19th century, Florence Nightangle advocated the necessity of
statistics and began collecting data systematically
• Bertillon Classification of cause of death was practiced in France in 19th
century
• In 1940, WHO advanced Bertillon's system and released International
Statistical Classification, Injuries and Causes of Death (ICD – 1)
• Similarly, different versions and sub versions of ICD were released in
different dates
• After 18 years of ICD 10, WHO released ICD 11 in 18 June, 2018

ICD - 11
• ICD 11 is internet based
• There is no necessity of modification by different countries to implement ICD – 11
• It comes with implementation package including transition tables from ICD 10, a
translation tool, a coding tool, web services, a manual, training material and
many more.
• It was developed by 300 specialists from 55 countries, organized in 30 main
working groups.
• It is much easier and user friendly than ICD 10
• It has 55,000 codes.
• It has given effort in antimicrobial resistance and global antibiotic resistance
surveillance system
• It has new chapters including traditional medicine and sexual health, which is
addition to ICD 10.

ICD - 11
• 01 – Certain infectious or parasitic diseases
• 02 – Neoplasms
• 03 – Diseases of blood or blood – forming organs
• 04 – Disease of the immune system
• 05 – Endocrine, nutritional or metabolic disease
• 06 – Mental, behavioral or neurodevelopmental disorder
• 07 – Sleep – wake disorder
• 08 – Disease of the nervous system

Cont. …
• 09 – Disease of the visual system
• 10 – Disease of the ear or mastoid process
• 11 – Disease of the circulatory system
• 12 – Disease of the respiratory system
• 13 – Disease of the digestive system
• 14 – Disease of the skin
• 15 – Disease of the musculoskeletal system or connective tissue
• 16 – Disease of the genitourinary system

Cont. …
• 17 – Conditions related to sexual health
• 18 – Pregnancy, childbirth or the puerperium
• 19 – Certain conditions originating in the perinatal period
• 20 – Developmental anomalies
• 21 – Symptoms, signs or clinical findings, not elsewise classified
• 22 – Injury, poisoning or certain other consequences of external
causes
• 23 – External causes of morbidity or mortality
• 24 – Factors influencing health status or contact with health services

Cont. …
• 25 – Codes of special purpose
• 26 – Supplementary Chapter Traditional Medicine Conditions –
Module I
• V Supplementary section for functioning assessment
• X Extension Codes
Please refer the link:
https://icd.who.int/browse11/l-m/en

Descriptive Epidemiology: Distribution of Disease
Characteristics of Time, Place and Person
• DE is inexpensive and less time consuming than analytic studies.
• DE describes pattern of disease occurrence in terms of
• Time
• Person
• Place
• Data provided are useful for
• Public health administrators (for allocation of resources)
• Epidemiologists (first step in risk factor determination)

Three categories of DE clues
• Time: When is the sickness occurring?
• Person: Who is getting sick?
• Place: Where is the sickness occurring?

Time distribution – Secular Trend
• Gradual change in the frequency of disease over long period of time.
• Eg. Tetanus in US from 1955 – 2000. During 2000, a total 35 cases of
tetanus was reported. The percentage of cases among persons aged
25 – 59 years has increased in last decade while tetanus vaccine was
available in 1933.

Time distribution – Periodic Trend
• Temporal interruption of the general trend of secular variation.
• Sometimes, periodic trend is also recognized as seasonal trend.
• When the variation is over a year, it is generally known as
seasonal/cyclic trend.
• Eg. Wooping cough – Four monthly admission, 1954 – 1973

Time distribution – Cyclic (Seasonal) trend
• Many phenomena (eg. Weather and health related) show cyclic trend.
• Cyclic/Sesonal trend increases and decreases in the frequency of a
disease or other phenomena over a period of several years or a year
(season).
• Generally, when the variation is less than a year, it is known as
periodic trend.
• Seasonal fluctuation is affected by: Environmental factors,
Occupational factors and Recreational activities.
• Eg. Pneumonia – Influenza Deaths.

Time distribution – Epidemics
• Pandemic: A worldwide epidemic affecting an exceptionally high
proportion of the global population.
• Endemic: The habitual presence (or usual
occurrence) of a disease within a given
geographic area.
• Epidemic: An increase in incidence above the
expected in a defined geographic area within a
defined time period. It is the occurrence of an
infectious disease clearly in excess of normal
expectancy, and generated from a common or
propagated source.

Person Distribution
• Age
• Sex
• Occupation
• Race/Ethnicity
• Socioeconomic status
• Education
• Marital status
• Residence
• Behavior
• …………

In local setting
Place distribution
• International (Pandemic)
• National
• Inner city variation, and
• Outer city variation
• Rural
• Urban

Thank you

Epidemiology v1.5 unit 1

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Epidemiology v1.5 unit 1