Transcript Epidemiology and its Applications

Prof. Saman Wimalasundera
MBBS DO PhD
Professor in Community Medicine
Former Head, Department of Community
Medicine
In charge Ophthalmologist
Community Ophthalmology center
Faculty of Medicine
University of Ruhuna
Galle
Sri Lanka
Epidemiology and
its application
The concepts of epidemiology were first
suggested by Hippocrates in the fifth century
B.C. that the development of human disease
might be related to external and personnel
environment of an individual.
The word epidemiology is derived from
Greek and means “Studies upon people”
Epi – Upon, Demos – People, Logia – Study
In contrast to clinical medicine epidemiology
involves the study of group of people rather
than individuals.
Epidemiologist vs.
clinician
A clinician identifies the ailment in his patients
using certain scientifically developed tools to
ascertain history of illness, clinical examination
and investigations.
Epidemiologist addresses the understanding
of the distribution and determinants of a
disease in a community (not an individual)
using standard parameters.
What constitute
epidemiology
Epidemiology includes:1. The methods for measuring the health of
groups and determining the attributes
and exposures that influence health.
2. The study of the occurrence of disease in
its natural habitat rather than in the
controlled environment of the laboratory.
3. The methods for the quantitative study of
the distribution, variation, and determinants
of health related outcomes in specific
groups (sub populations) of individuals, and
the application of this study to the
diagnosis, treatment, and prevention of
disease status or events.
Evolution of epidemiology
The evolution of medical sciences in its
earlier phase was based on curative
medicine. The primary objective was to cure
a patient of his illness. Doctors in historical
times looked at their patients as ill people
who needed some treatment.
Thus medical science was individual
oriented. But gradually it became evident
that better human health could be achieved
by prevention of diseases rather than by
cure.
A Historical Sketch
A Long sketch of time ran for more than 2
millennia from Hippocrates (470-400 B.C.) to
the first third of 19th century.
Hippocrates developed the medical
approach by providing concise, accurate and
complete description of actual clinical cases.
An Italian clinician called Bernardino
Ramazzini in 1700 moved from observation of
clinical cases to the consideration of ‘work
circumstances’ in similar cases. He is now
regarded as the founder of occupational
medicine. (Explained in his book. “De Morbis
Artificum Diatriba”).
The major step forward in epidemiology
occurred in 1662. John Graunt analyzed
the weekly reports of births and deaths in
London.
For the first time in the history, a quantified
pattern of disease, deaths and births was
Found. John Graunt is regarded as the
founder of demography now.
His observations were published in his
book. Named “ the nature and political
observations made upon the bills of Mortality”.
After two centuries William Farr (1839) a
physician was given the responsibility for
medical statistics in England and Wales. He
set up a system for routine compilation of vital
statistics and application of data for evaluation
of deaths.
Hippocrates, Ramzinni, Graunt and Farr
contributed to the understanding of disease
frequency and distribution.
Another British physician John Snow
formulated and tested a hypothesis concerning
the origins of an epidemic of cholera in London
on the basis of available descriptive data.
Snow postulated that cholera was
transmitted by contaminated water. (then
unknown mechanism)
He observed that death rates from Cholera
were particularly high in certain areas of
London.
Those areas were supplied with water
by two water companies namely “Lambeth”
and “Southwark & Vauxhall” in 1849. Both the
companies that time drew water from river
Themes at a point heavily polluted with sewage.
The Lambeth company then changed its
source to an area of Themes where the water
was quite free from sewage of London.
The rate of cholera deaths then declined in
those areas suppied by Lambeth company.
Death rates from cholera
According to water company supplying sub districts of
London
Water company
Population
in 1851
Southwark and
Vauxhall
Both companies
Lambeth
167, 654
Cholera
deaths in
18531854
192
Deaths
per
100,000
living
114
301, 149
182
60
14, 632
00
00
Concepts of epidemiology

Definitions
“Epidemiology is defined as the study of the
distribution and determinants of health related
status or events in specified populations and
the application of this study to control the health
problems” (Last 1988)
Applications of epidemiology
The epidemiology is useful in:
1. Search of cause/causes of disease/diseases.
2. Helps to describe the health status of
population or groups.
3. Helps to discover and bridge gaps in
natural history of diseases.
4. Helps in controlling the diseases. To break
the weakest link in chain of transmission of
communicable diseases and reducing non
communicable diseases.
5.
Helps in planning of health programs on
evidence basis and setting up of health
priorities.
6. Helps to evaluate health programs and
interventions.
7. Helps to determine the chances or
probability of occurrence of disease/
deaths and disability
8. Helps in better management of health
services and hospital services.
9. Helps to set-up cut-off levels between
normal and abnormal population and
establish trigger levels for action or
intervention.
Sources of
epidemiological
Measurements
1.
2.
3.
4.
5.
Cross sectional surveys
Medical records
Death certificate
Census
Organizational data
Domains of epidemiology

Descriptive epidemiology
Descriptive epidemiology is the most Basic form
of epidemiology. It is concerned with the description
of the patterns of occurrence of health-related status
or events in groups.
The determination of frequency and distribution of
disease, incidence, prevalence, and mortality rates
are included in descriptive epidemiology.

Analytical epidemiology
Analytical epidemiology is based on the
observations made in the descriptive
epidemiology. The design, execution and
analysis of subjects between groups helps
evaluate potential association between risk
factors and health outcomes to answer the
question “why?”.
Analytical epidemiology consists of
two types of research processes
1. Observational process
2. Experimental studies
Basic triads of descriptive and
analytical epidemiology
There are two different triads (3 essential
components) considered in studying different
sections
Descriptive
epidemiology
 Time (when)
Analytical
epidemiology
Host
Place
Agent

(where)
Person (who)

Environment
Triad of descriptive
epidemiology

Time





Changing or stable
Seasonal variations
Secular trends (long-term study of
incidence)
Point source or propagated
Cyclical variations (spikes of
incidences at regular intervals)
Triad of descriptive
epidemiology

Place




Geographically restricted or wide
spread
Relation to water and food supply
Multiple cluster involvement or one
Rural/Urban distribution
Triad of descriptive
epidemiology

Person





Age
Socio economic status
Gender
Ethnicity / Race
Behavior
Triad of analytical
epidemiology

Agent







Nutrients
Poisons
Allergens
Radiation
Physical trauma
Microbes
Psychological factors
Triad of analytical
epidemiology

Host factors




Genetic factors
Immunologic state
Age
Personal behavior
Triad of analytical
epidemiology

Environment



Overcrowding
Atmospheric changes
Modes of transmission
Vector
Vehicle
Reservoir

Clinical epidemiology
When periodic observations are made over
a long period of time in patients with a wide
spectrum of clinical manifestations of the
disease, a complete profile of the natural
history of the disease may be obtained.
This forms the basis of clinical epidemiology.
Epidemiology of diseases
Sri Lanka is said to be facing a double
disease burden due to communicable and non
communicable diseases (NCD) today.
What is triple burden???
The diseases burden in the country is given in
terms of (apart from basic measures)
1.Years of potential life lost
2.Life expectancy free from disability
3. Disability adjusted life years lost – DALYs
4.Quality adjusted life years lost - QUALYs
loss per 1000 population.
Country has to fight to control communicable
and non communicable diseases.
Epidemiology of communicable
diseases (CCD)

Definition :- Communicable disease
A communicable or infectious disease is an
illness caused by transmission of a specific
infectious agent or its toxic products from an
infected person or animal to a susceptible
host, either directly or indirectly through an
intermediate animal host, vector or inanimate
environment (Last 1995)
Disease Transmission
Man to man
Animal to man
What is an Epidemic?
It is the occurrence of cases of illness,
specific health related behavior or other
health related events clearly in excess of
normal expectancy in a community or region.
An Endemic disease
A disease that usually present in a
population or given area at a relatively high
prevalence and incidence rates in compared
to other areas.
E.g. Malaria is an endemic disease in
Polonnaruwa
Major emerging and re-emerging
infectious diseases
1.
2.
3.
4.
5.
6.
7.
8.
HIV/AIDS
Hepatitis B and Hepatitis C
Tuberculosis
Dengue
Malaria
Japanese encephalitis
Plague
Cholera
Major reasons for emergence of
infectious diseases










High population growth, uncontrolled and
unplanned urbanization,
Poor environmental sanitation,
Migration of population,
Natural disasters,
Growing international trade, tourism and rapid travel,
Alterations in microorganisms,
Resistance to antimicrobials,
Insecticide resistance,
Weak public health system.
Illiteracy and ignorance.
Chain of infection or chain
of transmission
Infectious agent
Transmission process
ENVIRONMENTS
Host
Infectious agent



Pathogenicity
Virulence
Infectivity
Transmission process
This is the second important link in the
chain of infection.
Transmission is defined as “Spread of
infectious agent through the environment or to
another person, from the reservoir and
source”.
Methods of transmission


Direct and
Indirect
Direct methods of
transmission








Touching
Kissing
Sexual intercourse
Child birth
Breast-feeding
Air borne, short distance via droplets
(by coughing, Laughing, sneezing, spitting).
Transfusion of blood
Transplacental from mother to fetus
Indirect transmission





Vehicle borne transmission (by
contaminated food and water)
Vector borne transmission
Parenteral by unsafe injection
Fomite transmission
Unclean hands
Control of communicable
diseases (CCD)-discuss
under 5 headings
1. Control of infectious agents in the
environments
2. Control of infectious agent in host
3. Control of outbreaks of CCD
4. Other measures
5. Specific measures for control of HIV
epidemic
(1) Control of infectious
agents in the environments

Controlling sources of infection
1.
Supply of safe drinking water by treatment and
chlorination of water, pasteurization of milk.
Safe disposal of human excreta and animal excreta by
sewerage system and sanitary latrines, compost
pits/manure pits.
Control vectors of diseases – by source reduction and
anti-larval and anti-adult measures.
Animals – vaccinate dogs against rabies and eliminate
street dogs.
Rodent control measures-trapping and killing
Hospital waste management
Disinfections
2.
3.
4.
5.
6.
7.
(2) Control of infectious
agent in host
1.
2.
3.
4.
5.
Reservoir control
Practice of chemoprophylaxis
Surveillance
Notification
Quarantine
1. Complete quarantine
2. Modified quarantine
6. Isolation
7. Education and behavior
(3) Control of outbreaks of
CCD-different steps will be
discussed later
Communicable diseases like Malaria,
JE, DHF , Hepatitis E & A, Hepatitis B and
Diarrhoeal diseases quite often occur in
epidemic proportion. Many local and focal
outbreaks are being reported quite frequently;
Hence, control of outbreaks of these diseases
is an essential requirement.
(4) Other measures
1. Legislation
Epidemic disease control act. And
notification helps control of CCD.
2. Observe international health
regulations
Notifiable diseases
Group A
•
•
•
Cholera
Plague
Yellow fever
Group B
•
•
•
•
•
•
•
Rubella
Diphtheria
Enteric fever
Food poisoning
Leptospirosis
Measles
Tuberculosis
•
•
•
•
•
Whooping cough
Acute anterior poliomyelitis
Simple continued fever of over seven
days
Dengue
Dysentery
• Encephalitis
• Human rabies
• Malaria
• Tetanus
• Typhus fever
• Viral Hepatitis
Epidemiology of noncommunicable diseases (NCD)
Non communicable diseases cover wide
range of heterogeneous conditions affecting
different organs and systems of different
socioeconomic groups.
Over the last two decades morbidity and
mortality due to cardiovascular diseases,
mental disorders, cancer and trauma have
been rising due to following causes.
Causes
1. Rise in life expectancy and increasing
number of senior citizens.
2. Changing life styles: Faulty diet, use of
alcohol, sedentary life-physical inactivity
and rising stress-leading to obesity and
stress related problems.
3. Exposure to environmental risk factors-air
pollution.
4. Use of tobacco
5. Increasing population and rise in
automobiles and trauma incidence.
Implications
In view of the chronic morbidity and high
cost involve in the management of noncommunicable diseases attention need to be
focused on prevention, early detection and
appropriate management. Further, these
diseases cause lot of disability and
dependency and disease burden.
Multi - factorial origin
Causes of NCD are multi-factorial. Range
of life styles: risk taking behavior, changing
dietary pattern, physical inactivity, use of
alcohol and tobacco and stress in life have
been incriminated.
Future
For non-communicable diseases throughout
the all levels of care so as to reduce morbidity
and mortality.
1. Well-structured information education and
communication for primary and secondary
prevention of NCD.
2. Reorientation and skill up gradation of
health care providers
3. Establishment of Referral linkages between
primary secondary and tertiary institution.
4. Production and provision of drugs for NCD.
5. Development of institution for rehabilitation
of disabled persons due to NCD, teaching
persons to live with their disability.
6. Development of hospices for terminally ill
people who cannot have home based care.
7. Creation of epidemiological database on
NCD especially, CVD’s, strokes and
diabetes.