2. Outlines
• Public health and Epidemiology
• Historical development of Epidemiology
• Dynamicity of diseases
• Natural history of diseases
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3. Public health
• Public health is “the science and art of
preventing disease, prolonging life and
promoting health through the organized
efforts and informed choices of society,
organizations, public and private,
communities and individuals (Winslow 1920)
• It links many disciplines and rests upon the
scientific core of epidemiology.
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4. Three core functions of Public health
– Assessment
– Policy and program
development
– Assurance
(implementation and
evaluation)
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5. Identifying Issues of Public Health
Importance
Consider:
• Magnitude of the problem: Incidence and
prevalence
• Seriousness of the problem: case fatality rate
• Availability of effective intervention: evidence of
effectiveness of interventions
• Impact of the disease on health, social, and
economic welfare
• Proportion of people potentially affected by the
disease
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6. Evidence Driven Public Health
• Good public health practice requires a
functional information system to guide
interventions and to inform the general
public.
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7. Sources of Information in public
health
Standard scientific methods
• Epidemiology
• Demography
• Health Services Research…
Other Methods
• Expert assessment
• Community assessment
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8. Clinical approach Vs Public health
approach
The clinical approach
• Deals with individuals, families.
• The provider's mission is to do what is best for the
patient.
The public health approach:
• In its ideal concept, deals with communities.
• Its mission is to serve the community, even when
particular individuals may well be disadvantaged in
some way
• The scope of public health is much broader than that of
the clinical approach
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9. A brief history of public health
• Community attempts to prevent and limit the
spread of disease go back to antiquity. For
example, religious traditions against eating pork
and shellfish reflect the special hazards of eating
those foods when inadequately preserved or
prepared.
• As often happens in public health, even without
an understanding of the underlying etiology
effective preventive measures can be taken.
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10. • By the 1600’s, the practices of isolation and
quarantine had begun to be employed to prevent
the spread of certain diseases;
• By the 1800’s these practices had become
common in the American colonies.
• Methods of smallpox inoculation also began to
be used and apparently mitigated some
epidemics, even before Edward Jenner's
introduction of a safe vaccine based on cowpox
virus.
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A brief history of public health
11. • With the 19th century came two dramatic
advances in the effectiveness of public health
– “the great sanitary awakening” Winslow,
quoted in The Future of Public Health (FPH)
and the advent of bacteriology and the germ
theory.
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A brief history of public health
12. Epidemiology
• The study of the distribution and determinants of
health related states and events in populations,
and the application of this study to control health
problems” [John M. Last, Dictionary of
Epidemiology])
• Epidemiology is the study of health and disease in
populations and comes from three Greek words
epi (among, upon), demos (people), and logy
(study)
• It’s a basic science of public health
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13. Definition of terms
• Study: Epidemiology involves systematic
collection, analysis and interpretation of
data
‘‘ Epidemiology is a science’’
• Frequency: Epidemiology studies the
number of times a disease occurs
• It answers the question How many?
‘‘Epidemiology is a quantitative science’’
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14. Definition of terms…..
• Distribution: Epidemiology studies
distribution of disease by person, place
and time
• It answers the question who , where and
when?
Epidemiology describes health events
(Descriptive Epidemiology)
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15. Definition of terms….
• Person (Who)
Young Vs Old
Female Vs Male
Rich Vs Poor
• Place (Where)
Lowland Vs Highland
Restricted or widespread (pandemic)?
Urban Vs Rural
• Time (When)
Day Vs Night - Point source or propagated.
Seasonal Variations
Long term variations
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16. Definition of terms….
• Determinants : Epidemiology searches for the causes
and other factors that influence the occurrence of
disease and other health-related events.
• It answers the question how and why?
How: mechanism
Mode of transmission
Why: cause
Genetic Vs environmental
Social and cultural conditions
Epidemiology analyses health events
(Analytic Epidemiology)
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17. Definition of terms….
• Diseases & other health related events
Epidemiology is not only the study of diseases
The focuses of Epidemiology are not only
patients, it studies all health related conditions
(injuries, infectious, non infectious etc)
‘‘Epidemiology is a broader science’’
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18. Definition of terms….
• Specified Human population
o The clinician’s “patient” is the individual;
o The epidemiologist’s “patient” is the community.
‘‘Epidemiology is a basic science of public health’’
• Application
o Epidemiology is not just “the study of” health in a
population;
o It involves the application of epidemiologic study
findings to control the health problems.
o Epidemiology is a science and practice
‘‘ Epidemiology is an applied science’’
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19. Fundamental Epidemiological
Assumptions
1. Human disease does not occur at random.
2. Human disease has causal and preventive
factors that can be identified through
systematic investigation.
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20. Raise of Epidemiology
• The birth of modern epidemiology occurred
during the 19th century and epidemic
investigations prior to the middle of that
century were mostly descriptive, rather than
etiologic in orientation.
• Peter Panum, however, investigated the 1846
measles outbreak on the Faroe Islands “much
the way an Epidemic Intelligence Service
Officer at CDC would today”
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21. Time line for the history of public
health and epidemiology.
Antiquity Concepts of health closely tied to religion (e.g., Old Testament)
Greek writers draw links to environmental factors (e.g., Hippocrates)
Romans associate plumbism with wine from lead-glazed pottery
1334 Petrarch introduces the concept of comparison and indeed of a clinical trial
1603 John Graunt – Bills of Mortality and the “law of mortality”. The first life table,
giving the probability of dying at each age
1700 Bernadino Ramazzini – “father of occupational epidemiology”; also breast
cancer in nuns
1706-1777 Francois Bossier de Lacroix (known as Sauvages) – systematic classification of
diseases (Nosologia Methodica)
1747 James Lind – scurvy experiment
1775 Percival Pott – scrotum cancer findings
1798 Edward Jenner – cowpox vaccination against smallpox
1787-1872 Pierre Charles Alexandre Louis (1787-1872) – the “Father of Epidemiology”, La
methode numerique
LaPlace, Poisson – the birth of statistics
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22. Time line for the history…..
1834 William Farr, William Guy, William Budd (all students of Louis) –
founded the Statistical Society of London
1847 Ignaz Semmelweiss (Vienna) – discovers transmission and prevention of
puerperal fever
1849 John Snow – waterborne transmission of cholera
1850 Epidemiological Society of London established
1851 John Grove – On the nature of epidemics (presented the germ theory)
Oliver Wendell Holmes and George Shattuck, Jr. (and Shattuck's student,
Edward Jarvis) – founded the American Statistical Society
Beginning of the era of bacteriology
1887 The Hygienic Laboratory, forerunner of the U.S. National Institutes of
Health, is created within the Marine Hospital Service in Staten Island, NY
1900 Yule – notion of spurious (i.e., nonsubstantive) correlations, “Simpson's
paradox”
1914-1918 Joseph Goldberger studies pellagra
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23. Time line for the history….
1920 Split between U.S. organized medicine and physicians interested in public health
(the latter were interested in national health insurance; public health concern vs.
individual concern)
1937 Austin Bradford Hill, Principles of Medical Statistics
1942 Office of Malaria Control in War Areas (in US; became Communicable Disease
Center (CDC) in 1946, Center for Disease Control in 1970, Centers for Disease
Control in 1980, and Centers for Disease Control and Prevention in 1992)
1948 World Health Organization (WHO)
1948 John Ryle becomes first chairman of social medicine at Oxford. Observed that
physicians have curiously little concern with prevention.
1950-
1970
Epidemiology successes – fluoride, tobacco, blood pressure and stroke, CHD risk
factors, toxic shock syndrome, Legionnaire's disease, Reye’s syndrome,
endometrial cancer and exogenous estrogens
1975 Lalonde Report (Canada)
1979 Healthy People U.S. and Health Objectives for the Nation
1988 U.S. Institute of Medicine Report of the Committee for the Study of the Future of
Public Health – Public health system is in “disarray” – AIDS, injuries, teen
pregnancies, Alzheimer's disease 23
24. Modes of investigation:
Descriptive vs. Analytic epidemiology
• Although the distinction is often difficult to
draw, in part because of the greater valuation
placed by many on the latter, epidemiologic
investigations are sometimes usefully
characterized as either descriptive or analytic
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25. Descriptive epidemiology
• Descriptive epidemiology describes the health
conditions and health-related characteristics of
populations, typically in terms of person, place,
and time.
• Answer the questions : Who?, Where? and,
When?
• This information serves as the foundation for
studying populations. It provides essential
contextual information with which to develop
hypotheses, design studies, and interpret results.
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26. Analytic epidemiology
• Analytic epidemiology involves the systematic
evaluation of suspected relationships, for
example, between an exposure and a health
outcome.
• Because of their narrower focus, analytic
studies typically provide stronger evidence
concerning particular relationships.
• Answer the questions: How? and, Why?
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27. Epidemiological study designs
DESCRIPTIVE
Dealing with population:
• Correlational or
ecological
Dealing with individuals:
• Case report or series
• Cross sectional survey
ANALYTIC
Observational studies:
• Case-control
• Cohort
Intervention studies:
• RCT
• Quasi experimental
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28. Using Epidemiology for Public Health
The iceberg phenomenon
Routine information comes mainly from people who attend the
health services
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Proper and unbiased assessment of health conditions is important for good
public health practice!!
34. What is happening? When? Where?
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Seasonal mortality rates by month per 1,000 person years at risk, by geographic area, over a ten-
year period (19987-1996). Butajira, Ethiopia. [Byass, Berhane, Emmelin et al 2001]
36. Key focuses for Epidemiological
Studies
• Quantitative (rather than qualitative)
• Observational (rather than experimental)
• Focus on determinants of disease in human
• populations (rather than individuals)
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37. Epidemiology functions and areas of
application
• Epidemiology is both a field of research to
advance scientific understanding and also of
application of knowledge to control disease
and advance public health, a (primarily
observational) science and a public health
profession.
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38. Epidemiology functions and areas of
application
• Thus, epidemiologists conduct research and also
work to control and prevent disease.
• Discover the agent, host, and environmental
factors that affect health, in order to provide the
scientific basis for the prevention of disease and
injury and the promotion of health.
• Determine the relative importance of causes of
illness, disability, and death, in order to establish
priorities for research and action.
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39. Epidemiology functions and areas …..
• Identify those sections of the population which have the
greatest risk from specific causes of ill health [and benefit
from specific interventions], in order that the indicated action
may be directed appropriately. (targeting)
• Evaluate the effectiveness of preventive and therapeutic
health programs and services in improving the health of the
population.
• Study the natural history of disease from its precursor states
through its manifestations and clinical course
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40. • Conduct surveillance of disease and injury
occurrence in populations and of the levels of risk
factors – passive (receive reports), active (poll
practitioners, conduct surveys)
• Investigate outbreaks (e.g., hospital-acquired
infections, disease clusters, food-borne and
water-borne infections) to identify their source
and controlling epidemics (e.g., measles, rubella,
coronary heart disease, overweight)
Epidemiology functions and areas…..
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41. Natural history of Diseases
• Diseases and other phenomena of interest in epidemiology
are processes.
• For example, the process by which bronchogenic lung
cancer arises involves a progression over many years of the
development of abnormal cells in the bronchial epithelium.
• Thus, defining, observing, and measuring health and
disease requires an appreciation of the concept of natural
history – the evolution of a pathophysiologic process.
"Natural" refers to the process in the absence of
intervention.
• Natural history encompasses the entire sequence of events
and developments from the occurrence of the first
pathologic change (or even earlier) to the resolution of the
disease or death on the absence of intervention.
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42. Important Time Intervals in the Natural History of an
Infectious Disease
Incubation period, Latent Period and the Serial Interval
Incubation Period – average length of time between infection
and the onset symptoms in each case
Latent Period – average length of time between infection and
the onset of transmissibility
Serial Interval – average length of time between a case being
infected and that case infecting subsequent cases (also called
the Generation Time) denoted Tg
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49. Depends upon the disease
• Influenza latent period < incubation period
• Varicella latent period < incubation period
• Malaria latent period > incubation period
• SARS latent period > incubation period
• HIV latent period << incubation period
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