presentation on Natural history of disease and concepts of prevention

1. CONCEPT OF NATURAL HISTORY OF DISEASE AND
LEVELS OF PREVENTION
BY DR. NAVEEN SHYAM R
JUNIOR RESIDENT
DR. SUSHILA NAYAR SCHOOL OF PUBLIC HEALTH
(INCORPORATING THE DEPARTMENT OF COMMUNITY MEDICINE)
MGIMS, SEWAGRAM, WARDHA, MAHARASHTRA, INDIA

2. DEFINITION
Natural history of disease signifies the way in which
a disease evolves over time from the earliest stage
of its pre-pathogenesis phase to its termination
as recovery, disability or death in absence of treatment or
prevention.

3. The natural history of disease is best established by cohort
studies.
As these studies are costly and laborious, understanding of the
natural history of disease is largely based on other epidemiological
studies, such as cross-sectional and retrospective studies,
undertaken in different population settings.

5. Tuskegee Study
1. In 1932, the Tuskegee Institute, USA began a study to record the
natural history of syphilis in hopes of justifying treatment programs
for blacks.
2. The men were never given adequate treatment for their disease.
Even when penicillin became the drug of choice for syphilis in 1947
3. The 40-year Tuskegee Study of Untreated Syphilis in the African
American Males was a major violation of ethical standards.
4. After this , ethical consideration like informed consent became more
than mandatory for any research

6. MODELS OF DISEASE CAUSATION
WEB OF
CAUSATION
THEORY
BEING’S MODEL
EPIDEMIOLOGICAL
TRIAD
GERM THEORY OF
DISEASE
1878
MIASMA THEORY
500BC
WHEEL THEORY
1985

7. MIASMA THEORY
History of disease causation goes back to
Miasma theory
 It says “ diseases such as cholera, chlamydia or black death is
caused by Miasma”, means bad air
 It was most accepted theory till 19th century when it was
replaced by Germ theory of disease.

8. GERM THEORY OF DISEASE
Germ theory of disease was first proposed in 1546 by
Girolamo Fracastro
 Louis Pasteur proved that the diseases are caused by organisms
in 19th century
According to germ theory of disease “ one to one
relationship between casual agent and disease”

9. WEB OF DISEASE CAUSATION
The model of disease causation was suggested by Mac Mahan
and Pugh.
It is ideally suited in the study of chronic disease that states that
disease is the out come of interaction of multiple factors.
This theory does not imply that the disease cannot be controlled
unless all the multiple causes.

10. WEB OF CAUSATION CONCEPT

11. EPIDEMIOLOGICAL TRIAD
Epidemiological Triad theory
states that:
“an external agent can cause
diseases on
a susceptible host when
there is a
conducive environment”

12. EPIDEMIOLOGICAL TETRAD
Agent
Host
Environment
Time

13. FLOW CHART OF NATURAL HISTORY

14. TWO PHASES OF NATURAL HISTORY OF DISEASE
PRE-PATHOGENESIS PHASE
Start when the conditions favoring a disease are present but the
agent hasn’t entered the body.
We all are in pre pathogenesis phase of many communicable and
non communicable diseases
This situation also referred to as “man exposed to the risk of the
disease”

15. PATHOGENESIS PHASE
 Begins with entry of the organism
 Characterized by presence of cases as clinical or sub clinical.
 Pathogenic phase decides the fate of disease outcome as
recovery, disability or death
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16. AGENT FACTORS
Disease Agent is defined as a substance
living or non living or a force tangible or
intangible, the excessive presence or relative lack of which is the
immediate cause of a disease.

17. AGENT FACTORS: CLASSIFICATION
BIOLOGICAL
AGENT
-BACTERIA
-VIRUSES
-FUNGI
CHEMICAL
AGENT
-SMOKE
-ALCHOHOL
-POISON
PHYSICAL
AGENT
-TRAUMA
-RADIATION
-FIRE
NUTRITIONAL
AGENT
-UNDER
NUTRITION
-OVER
NUTRITION

18. HOST FACTORS (INTRINSIC)
In epidemiological terminology the
human host is referred to as soil and
the disease agent as seed.
In some situations, host factors play
an important role in determining the
outcome of an individual’s exposure
to infection
AGE
SEX
RACE
CULTURE
OCCUPATION
GENETIC
PROFILE

19. ENVIRONMENTAL FACTORS (EXTRINSIC)
The study of disease is really the
study of man and his environment
It is defined as,
“ All that which is external to the
individual human host living or non
living and with which he is in constant
interaction”
3 TYPES OF
ENVIRONMENT
1. PHYSICAL
ENVIRONMENT
2. BIOLOGICAL
ENVIRONMENT
3. PSYCHOSOCIAL
ENVIRONMENT

20. RISK FACTORS
Risk factors are defined as
“ An attribute or exposure that is significantly associated with
the development of a disease”
or
“A determinant that can be modified by intervention there by
reducing the possibility of occurrence of disease or other
specified outcomes”.

22. CAUSE Vs RISK FACTOR

23. RISK GROUPS
WHO developed and promoted the approach to identify precisely
the “risk groups” or “target groups” in the population by certain
defined criteria and direct appropriate action to them first. This is
called “risk approach ”.
Age, Sex, Physiological state, Genetic factorsBIOLOGICAL SITUATIONS
Rural, Urban slums, overcrowding, proximity to industriesPHYSICAL SITUATIONS
SOCIOCULTURAL AND CULTURAL SITUATIONS

24. SPECTRUM OF DISEASE
Spectrum of disease is a graphic
representation of variations in the
manifestations of disease.
At one end of the disease
spectrum are subclinical infections
In the middle of the spectrum lie
illness ranging in severity from mild
to severe
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25. ICEBERG OF DISEASE

26. CONCEPTS OF PREVENTION
 Prevention is the process of intercepting or opposing the “cause”
of a disease and thereby the disease process.
Levels of prevention :-
1. Primordial prevention
2. Primary prevention
3. Secondary prevention
4. Tertiary prevention

27. PRIMORDIAL PREVENTION
It is the prevention of the emergence or development of risk
factors in population groups in which they have not yet appeared.
The main intervention in primordial prevention is through
individual and mass education.

28. EXAMPLE OF PRIMORDIAL PREVENTION
Many adult health problems(e.g., obesity and hypertension) have
their early origin in childhood, so efforts are directed towards
encouraging children to adopt healthy lifestyles( e.g., physical
exercise, healthy dietary habits etc.)

29. PRIMARY PREVENTION
It can be defined as “ action taken prior to the onset of disease,
which removes the possibility that a disease will ever occur.”
It signifies intervention in the pre-pathogenesis phase of a disease
Two types of strategies :-
- Population (mass) strategy
- High risk strategy

30. Population strategy :-
Directed at whole population irrespective of the individual risk
levels and socio-economic, behavioral and lifestyle changes.
High risk strategy :-
Includes identification of “High risk groups” in the population and
bring preventive care to these risk group.

31. Two types of modes of intervention:
 Health promotion – It is the process of enabling people to control
over, and to improve health.
- Health education
- Environmental modifications
- Nutritional interventions
- Lifestyle and behavioral changes

32. Specific protection :- e.g.
- Immunization
- Chemoprophylaxis
- food fortification e.g., iodized salt
- Protection against occupational hazards
- Protection against accidents e.g., use of helmets
- Avoidance of allergens etc.

33. SECONDARY PREVENTION
Secondary prevention can be defined as “ action which halts the
progress of a disease at its incipient stage and prevents
complications.” It reduce the prevalence of the disease by
shortening its duration
It is applied in the early pathogenesis stage of disease.

34. It may also protect others in the community from acquiring the
infection and thus provide, at once, secondary prevention for the
infected individuals and primary prevention for their potential
contacts.
The specific interventions used is :- Early diagnosis and treatment

35. EARLY DIAGNOSIS
Defined as “ the detection of disturbances of homoeostatic and
compensatory mechanism while biochemical, morphological and
functional changes are still reversible”
E.g -
-Screening for disease for breast cancer (using mammography)
and cervical cancer (using pap smear).
-Medical examinations of school children, of industrial workers
and various disease screening camps.

36. TERTIARY PREVENTION
These include all measures undertaken when the disease has
become clinically manifest or advanced, with a view to prevent or
delay death, reduce or limit the impairments and disabilities,
minimize suffering and to promote the subject’s adjustment to
irremediable conditions.
Tertiary prevention has two types of approaches :
-Disability limitation
-Rehabilitation

37. DISABILITY LIMITATION:
These include all measures to prevent the occurrence of further
complications, impairments, disabilities and handicaps or even
death.
Example- Complete rest, morphine, oxygen and streptokinase is
given to a patient of Acute MI, to prevent death or complications
like arrhythmias / CHF.
-Application of plaster cast to a patient who has suffered Colle’s
fracture

38. IMPAIRMENT
• Any loss or
• abnormality of
• psychological,
• physiological or
• anatomical structure
• or function.
• Eg-Loss of foot
DISABILITY
• The inability to carry
• out certain activities
• because of
• impairment, that are
• considered normal
• for his age and sex.
• Eg-Cannot walk
HANDICAP
• The inability to
• discharge the
• obligations required
• of him and play the
• role expected of him
• in the society
• Eg-Unemployed

39. REHABILITATION
Defined as the combined and coordinated use of medical,
social, educational and vocational measures for training and
retraining the individual to the highest possible level of
functional ability.
SOCIALVOCATIONAL PSYCHOLOGICALMEDICAL
Restoration of
function
Restoration of
the capability to
earn a livelihood
Restoration of
family and social
relationships
Restoration of
personal dignity
and confidence

40. Examples of Rehabilitation are:
- Establishing schools for blinds
- Provision of aids for the handicapped
- Reconstructive surgery in leprosy
- Muscle re-education and graded exercises in neurological
disorders