01 Introduction to Epidemiology and health

about health

1. Introduction to Public Health
Kehabtimer Shiferaw
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2. Health
•The WHO defines health as ‘a state of
complete physical, mental, and social well-
being and not merely the absence of disease,
or infirmity’.
•Public health is the science and art of
preventing disease, prolonging life and
promoting health
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3. Introduction to Epidemiology
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4. Learning objective
•At the end of the session students should be acquainted with:
–The definition and scope of Epidemiology,
–Basic assumptionand unique characteristicsof Epidemiology,
–Historyand evolutionof Epidemiology,
–Theoriesof disease causation,
–Levels of disease prevention
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5. What’s Epidemiology?
•The term "epidemiology" springs directly from ‘epidemic’ which
originally referred to communicable disease outbreaksin humans.
•Epidemic is derived from the Greek words epi(upon) and demos
(people).
•i.e. Epidemiology is the study of what's ‘upon the people’
•ClassicallyEpidemiology is defined as:
‘The study of the frequency, distributionand determinantsof
diseases and health-related problems in humanpopulations and
the application of this study to the control of health problems’
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6. What’s Epidemiology? Cont….
•Frequency: Quantificationof the occurrence of diseases/health-
related problems.
•Distribution: Pattern of occurrence by place, personand time.
–Geographical distribution
–Temporal variation (seasonal, short period, secular trend)
–Pattern according to the typeof person most /least affected
•Determinants: Answers the question ‘why specific individuals are
affected/not affectedby the condition?’ What ‘risk factors’ are
‘causing’ this?
•Health related problems: This includes injuries, malnutrition, vital
events, health related behaviors, life style, and pertinent social
factors.
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7. What’s Epidemiology? Cont….
•Risk Factor: An individual attribute (intrinsic characteristic of the
individual) or exposure (externalenvironmental situation) that can
negativelyaffect health
•Cause: Factor necessary for the diseaseto occur and in its absence
that specificdisease can’t occur.
•It is also known as Etiologic agent.
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8. Classification of Epidemiology
•Descriptive Epidemiology:
–Is concerned with describing the frequency of the
disease/health-related phenomena by place, person and time.
–It is important for planning, priority setting and resource
allocationfor health interventions.
•Analytic Epidemiology:
–Investigates the etiology and risk factors of disease/health
related conditions.
–Also helps to investigate how specific therapies/interventions
prevent /control health problems (Experimental Epidemiology).
–Also helps to evaluate preventive/curative interventions
(Evaluative Epidemiology).
–Important for designing of prevention and control strategies.
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9. Purpose/Objectives of Epidemiology
1.To determine the extent /burden of disease in a community or
beyond
2.To study the natural history and progression of disease
3.To identify the cause and risk factors of disease
4.To evaluate both existing and new preventive and therapeutic
measures for a disease or condition
5.To provide the foundationfor providing servicesand developing
programsand policies
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10. Stages of epidemiological reasoning
•Specially in analytic epidemiology, epidemiologists use a two-stage
sequence of reasoning :
1.Determination of a statistical association b/n the
characteristics and the outcome (statistical inference)
2.The derivation of causal inference from such pattern of
statistical association
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11. The Discipline of Epidemiology
•Because health is multifaceted, epidemiology is interdisciplinary.
•It is extensively connected to the biomedical sciencessuch as
medicine, microbiology, physiology and pathology;
•Its quantitative nature connect it with statistics (more precisely
Biostatistics) and Demography.
•Many diseases have environmental origin, the study of life in
relation to the environment is ecology, so epidemiology is also the
science of the ecology of disease.
•Recent advancements are linking it with laboratory sciences
•In the search for solutions to health problems, epidemiology is
often cast beyond these traditional boundaries to social and
behavioral sciences.
•Hence epidemiology is bio-social-environmental science focusing
on disease in populations 11

12. Why we study Epidemiology?
•Epidemiology provides comprehensive information for:
–Understandingof diseases
–Identification of priorityhealth problems
–Hypothesisgeneration and testing
–Provision of evidence based care
–Designing of disease control and prevention strategies
–Evaluationof health programs
–Provides the methodologyfor understanding and planning,
conducting, analyzing, interpreting and presenting scientific
data.
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13. Basic Assumptions of Epidemiology
•The two fundamental assumptions of epidemiology are:
–Human disease doesn’t occur at random and
–Human disease has causal and preventive factors that can be
identified through scientific investigation.
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14. Unique Characteristics of Epidemiology
1.Studies are conducted on human population
2.Allows the quantificationof the magnitude of relationship
between exposure and disease
3.Provide information on how to prevent disease and alter risk
through interventions
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15. History of Epidemiology
•Hippocrates (460-377 BC):
–The epidemiologic way of thinking originated in writings
ascribed to the Greek philosopher-physician Hippocrates.
–In his book entitled ‘Air, Waters and Places’, he displayed an
extraordinary awareness of the impact of environment
(geography, water, climate, housing) on personal well-being.
–In doing so, he identified forces that epidemiologists today
recognize as major determinants of human health.
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16. History Cont….
•Claudius Galen (129-199):
–Known as father of Experimental Physiology.
–In epidemiology he described the importance of ‘innate
qualities of human body’, lifestyleand personalityin disease
causation.
–He also argued that diseases were caused by Miasma (Bad air)
from waste, stagnant water and dead animals.
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17. History Cont….
•GerolamoFrancastorius(1478-1553):
–An Italian presented the first coherent germ theory of disease
–He theorized that a variety of diseases are caused by
transmissible, self-propagating entities
–He thought that these agents were specific to each disease
and could spread from person-to-person or through infected
articles (fomites) or at a distance
–He argued that treatment should consist of the destruction of
the entities by either heat or cold or of their evacuationfrom
the body, or by neutralizing them by antagonistic substances
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18. History Cont….
•John Graunt(1620–1674):
–Regarded as the founder of Demography.
–He was the first to take a major step forward to quantify
patterns of birth, death and diseaseoccurrence.
–His observations upon the Bills of Mortality (1662)were based
on a series of weekly bills covering individual deaths and their
causes in the London area back to 1603.
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19. History Cont….
•James Lind (1716-1794):
–Carried out experimental study on the etiology and treatment
of scurvy.
–While he was a British navy physician he observed sailors were
developing a deadly bleeding disorder (scurvy) on long
voyages.
–He selected 12 men from the ship suffering from scurvy, and
divided them into six pairs, giving each group different
additions to their basic diet
–Treatments were: fermented alcohol made from apple juice,
sulfuric acid solution, seawater, spicy paste of garlic and
mustard, vinegar (acetic acid solution) and citric fruits.
–Demonstrated that citrus fruits (orange and lemon) cure scurvy
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20. History Cont….
•AlexandreLouis (1787-1872):
–A French physician, known for introducing the use of the
‘numerical method’in the field of medicine.
–He argued that the concept that knowledge about a disease
(natural history, clinical presentation and treatment) could be
derived from aggregated patient data.
–He also numerically demonstrated that bloodlettingwas an
ineffective treatment for the various fevers.
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21. History Cont….
•William Farr (1807–1883):
–He introduced a national system of recording causes of death
in Britain.
–He himself first analyzedthe data with great skill.
–He was instrumental in building up a classification of diseases
for statistical purposes.
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22. History Cont….
•John Snow (1813–1858):
–Known as the father of Modern Epidemiology
–He investigated the two epidemics of Cholera occurred in
Londonin 1849 and 1854.
–Based on descriptive datahe suspected the epidemic has
something to do with the drinking water source of the city.
–He postulatedthat the cholera was transmitted by a
contaminated water through unknown mechanism.
–He compared the Cholera mortality pattern across the drinking
water sources of London.
–He found out that the mortality rate was 10 times lower for the
districts supplied by the Lambethcompany compared to those
supplied by Southwarkand Vauxhall company. 22

23. History Cont….
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24. History Cont….
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25. History Cont….
–He also demonstrated that the epidemics was particularly high
in districtssupplied by both companies using water drawn
from the heavily polluted part of Themes river.
–Accordingly the Lambethco changed it water source to the
less contaminated part of the river and that was followed by
reduction in the occurrence of the epidemic.
–In doing so he demonstrated how hypothesis can be
generatedfrom descriptive epidemiology and how it can be
testedand applied for public health benefit.
–Note that J Snow’s observation came before the identification
of Vibriocholerae.
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26. History Cont….
•Joseph Goldberger (1874–1929):
–An American physician was a well known advocate for scientific
and social recognition of the links between poverty and
disease.
–In 1914 he investigated the cause of Pellagraand demonstrated
the disease was associated with diet rather than infection
agents.
–He conducted restricted-diet experiments on prisoners to show
that individuals who heavilyconsumed corn-based diets were
at a greatly increased risk of contracting pellagra.
–The investigation was made two decades before the
identification of niacin as the cause of pellagra.
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27. History Cont….
•Elizabeth Lane-Claypon(1877–1967):
–An English physician and one of the founders of the science of
epidemiology,
–Pioneeredthe use of retrospective Cohortand Case-control
studies.
–In 1912, she published a ground-breaking study of two cohorts
of babies, fed cow’s milk and breast milk respectively to
demonstrate the importance of BF for child growth.
–In 1923, she studied factors associated with breast cancer by
comparing 500 women with a history of breast cancer with
another 500 women who were free of the disease.
–The technique nowadays is known as Case-control Study.
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28. History Cont….
•Streptomycin trial for treatment of TB (1946–1947):
–The British Medical Research Council conducted one of the
first modern experimental studies on the use of streptomycin
to treat pulmonary tuberculosis.
–The trial was bothdouble-blindandplacebo-controlled.
–Generally accepted as the first randomized clinical trial.
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29. History Cont….
•Framingham Study (1947 till date):
–The study began with 5,000 adult subjects from Framingham,
Massachusettsand its now on 3
rd
generation of participants.
–Widely acknowledged as a premier longitudinal study.
–Focuses on risk factors of cardiovasculardisease.
–It is undisputedly the foundation stone for current ideas about
risk factors of CVD.
–Like the work of Doll and Hill, the Framingham Study is notable
for bringing about a shift in the focus of epidemiology from
infectious to noninfectious diseases.
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30. History Cont….
•Richard Doll (1912–2005) and Bradford Hill (1897-1991):
–In 1950 they showed that smokingwas an important cause of
lung cancer through a case-controlstudy.
–Later they also conducted a long-term prospective studyon
smoking and health
–Bradford Hill pioneered the first randomized clinical trial
(Streptomycin Tuberculosis trial)
–In 1965 he developed criteria for assessing evidence of
causation.
–Richard Doll did pioneering work on the relationship
between radiation and leukemia as well as that between
asbestos and lung cancer, and alcohol and breast cancer.
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31. History Cont….
•Field trial of theSalk polio vaccine (1954):
–The biggest epidemiological experiment till date
–Headed by Dr. Jonas Salk who developed the dead polio virus
–More than 600,000 children were injected with vaccine or
placebo,
–And more than a million others participated as “observed”
controls.
–Firmly establishing the efficacy of the killed virus vaccine and
paving the way for eradication of the disease,
–Later Dr. Albert Sabin conducted another large scale polio trial
on his attenuated vaccine (1957)
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32. Theories of Disease Causation
1.Supernatural theory:
–Stated that all disease caused by supernatural forces
–i.e. either the curse of god or due to evil force of demons
–Disease prevention was based on religiouspractices.
2.The Hippocrates theory
–Environmental factors have effects on ‘personal well-being’
3.The miasma theory:
–Attributed disease to bad odor or air.
–This model had been used to explain epidemicsof diseases
like cholera, plague, and malaria.
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33. Theories of Disease Causation Cont…
4.Contagion theory:
–Assumes that all diseases are contagious (communicable)in
nature.
–Isolation of people, and avoiding contact with cases were the
prominent preventive measures.
5. The germ theory:
–Is a theory which proposes that microorganismsare the
cause of many (if not all) diseases.
–Although highly controversial when first proposed, it has led
to the innovations and development of antibiotics, vaccines
and hygienic practices.
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34. Theories of Disease Causation Cont…
6. The epidemiological triad theory:
–This theory states that causation of disease is the function of
the environment, causative agents and host factors.
–Still an important model for infectious diseases.
7. Multi-causal theory:
–The most recent model of disease causation
–Has different sub-variants including the causal pie and the
web-causal theory
–Web-causal theory states that diseases are caused by a
function of different factors like socio-cultural factors,
political factors, environmental factors etc.. beyond the
direct causes of diseases.
–Example: see the next slide.
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35. Theories of Disease Causation Cont…
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36. Level of Disease Prevention
•Disease prevention is any intervention that seeks to reduce or
eliminate diagnosable conditions.
•However in a broader sense, it is defined as any measure which is
directed to interrupt or slow progress of disease.
•Disease prevention is classified into the following four levels.
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37. Level of Disease Prevention Cont…
1. PrimordialPrevention:
–This aims at the establishment and maintenance of conditions
that minimize hazard to health.
–Its actions are measures that inhibit the emergence and
establishment of social and economic conditions that are
known to contribute to an elevated risk of disease.
–It is directed before the initiation of the disease.
–Its target can be the general population or selected groups.
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38. Level of Disease Prevention Cont…
2. PrimaryPrevention:
–This aims at the prevention of the incidence of disease.
–Its actions are focused on the protection of health by personal
and community wide efforts (example: preserving good
nutritional status, immunization, environmental hygiene,
modification of risk factors of chronic diseases, etc.).
–Its directed before the initiation of disease.
–Its target can be the general population or selected risky
groups.
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39. Level of Disease Prevention Cont…
3. SecondaryPrevention:
–This aims at cure of disease and prevention of more serious
consequencesthrough early detection and treatment.
–Example: early detection and treatment of trachoma patients,
screening for chronic diseases.
–In PH context, secondary prevention also results in reduction
of prevalence of the disease and risk of transmission.
–It is directed at the earlier stage of the disease (before usual
time of diagnosis).
–Its target is cases at pre-diagnosable condition.
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40. Level of Disease Prevention Cont…
4. Tertiary Prevention:
–This is intended to reduce, mitigate or limit progress or
exacerbation of diagnosed disease
–Is an important aspect of therapeutic and rehabilitative
medicine.
–Its target population is established patients.
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