Prevention and control

1. Principles of Disease Prevention &
Control of Communicable Diseases
Dr Khem R Sharma
AP, SPH&CM

2. Introduction
• Goals of medicine: to promote health, to preserve health, to restore
health when it is impaired, and to minimize suffering and distress
which are embodied in the word ‘Prevention’
• Successful prevention depends on the knowledge of causation,
dynamics of transmission, identification of risk factors/risk groups,
availability of prophylaxis and early detection and treatment
measures and to identify groups/population for continuous
evaluation & development of procedures that are applied

3. Levels of Prevention
• Prevention is defined in terms of four levels

4. Primordial prevention
• Primary prevention in its purest sense: - prevention of the emergence
or development of risk factors in countries or population groups in
which they have not yet appeared.
• Eg: many adult health problems (e.g., obesity, htn) have their early
origins in childhood, because this is the time when lifestyles are
formed (for example, smoking. eating patterns, physical exercise).
• Efforts are directed towards discouraging children from adopting
harmful lifestyles and promotion of healthy eating habits.
• The main intervention is through individual and mass education

5. Primary prevention
• Action taken prior to the onset of disease, which removes the possibility
that a disease will ever occur
• Signifies intervention in the in the pre-pathogenesis phase of a disease or
health problem (e.g., low birth weight) or other departure from health
• Primary prevention may be accomplished by measures designed to
promote general health and well-being, and quality of life of the people or
by specific protective measures
• It includes the concept of "positive health“ - that encourages achievement
and maintenance of "an acceptable level of health that will enable every
individual to lead a socially and economically productive life”

6. Primary prevention…
• WHO has recommended the following approaches for the primary
prevention of chronic diseases where the risk factors are established
1) Population (mass) strategy
• directed at the whole population irrespective of individual risk levels.
• For example, studies have shown that even a small reduction in the
average blood pressure or serum cholesterol of a population would
produce a large reduction in the incidence of cardiovascular disease
• The population approach is directed towards socio-economic,
behavioural and lifestyle changes

7. Primary prevention…
2) High-risk strategy
• It aims to bring preventive care to individuals at special risk.
• It requires detection of individuals at high risk by the optimum use of
clinical methods.
• Industrialized countries succeeded in eliminating a number of
communicable diseases like cholera/typhoid/dysentery and controlling
several others like plague/leprosy/tuberculosis by raising the standard of
living (primary prevention) and NOT BY MEDICAL INTERVENTIONS
• Much of these successes came even before immunization became universal

8. Primary prevention…
• It is a "holistic" approach that relies on measures designed to
promote health or to protect against specific disease "agents" and the
hazards in the environment.
• The safety and low cost of primary prevention justifies its wider
application and recently it is identified with "health education" and
the concept of individual and community responsibility for health
• To acheive an impact on the population, all the above three
approaches (primordial prevention, population strategy and high-risk
strategy) should be implemented as they are usually complementary

9. Secondary prevention
• Action which halts the progress of a disease at its incipient stage and
prevents complications - mainly the domain of clinical medicine
• The specific interventions are early diagnosis (eg., screening tests,
case finding programs) and adequate treatment
• It attempts to arrest the disease process; restore health by seeking
out unrecognized disease and treat it before irreversible pathological
changes have taken place; and reverse communicability of infectious
diseases
• It may also protect others in the community from acquiring the
infection and thus provide secondary prevention for the infected
individuals and primary prevention for their potential contacts

10. Secondary prevention…
• Drawback: the patient has already been subject to mental anguish,
physical pain; and the community to loss of productivity which are
not encountered in primary prevention.
• Imperfect tool in the control of transmission of disease and is often
more expensive and less effective than primary prevention
• In the long run, human health, happiness and useful longevity will be
achieved at far less expense with less suffering through primary
prevention than through secondary prevention

11. Tertiary prevention
• All measures available to reduce/limit impairments and disabilities,
minimize suffering caused by existing departures from good health
and to promote the patient's adjustment to irremediable conditions
• When the disease process has advanced beyond its early stages,
treatment, even if undertaken late in the natural history of disease,
may prevent sequelae and limit disability
• Tertiary prevention signifies intervention in the late pathogenesis
phase and extends the concept of prevention into the domains of
rehabilitation
• Modern rehabilitation includes psychosocial, vocational, and medical
components based on team work from a variety of professions

12. Natural History of Disease

13. Modes of Intervention
• Intervention can be defined as an attempt to intervene or interrupt the usual
sequence in the development of disease in humans
• Five modes of intervention have been described which form a continuum
corresponding to the natural history of any disease
1) Health promotion
• process of enabling people to increase control over, and to improve health
• Not directed against any particular disease, but is intended to strengthen the host
through a variety of approaches/interventions
• The well-known interventions in this area are:
i. health education
ii. environmental modifications
iii. nutritional interventions
iv. lifestyle and behavioural changes

14. 1) Health promotion
i. Health Education: one of the most cost effective interventions where a
large number of diseases could be prevented with little or no medical
intervention if people were adequately informed about them and if they
were encouraged to take necessary precautions in time.
ii. Environmental modifications: Comprehensive approach requires
modifications, such as provision of safe water; installation of sanitary
latrines; control of insects and rodents; improvement of housing, etc.
- History of medicine has shown that many infectious diseases have been successfully
controlled in western countries through environmental modifications, even prior to the
development of specific vaccines or chemotherapeutic drugs.
iii. Nutritional interventions: These comprise food distribution and nutrition
improvement of vulnerable groups; child feeding programs; food
fortification; nutrition education, etc.

15. 1) Health promotion…
iv. Lifestyle and behavioural changes: one of individual and
community responsibility for health
- Health education is a basic element of all health activity which is
of paramount importance in changing the views, behaviour and
habits of people
• A well-conceived health promotion program would first attempt to
identify the "target groups" or at-risk individuals in a population and
then direct more appropriate message to them

16. 2) Specific protection
• Currently available interventions aimed at specific protection include
1) Immunization
2) Use of specific nutrients
3) Chemoprophylaxis
4) Protection against occupational hazards
5) Protection against accidents
6) Protection from carcinogens
7) Avoidance of allergens
8) Control of specific hazards in the environment, eg., air pollution, noise control
9) Control of consumer product quality and safety of foods, drugs, cosmetics,

17. 3) Early diagnosis and treatment
• WHO - the detection of disturbances of homoeostatic and compensatory
mechanism while biochemical, morphological, and functional changes are
still reversible - very important in chronic diseases
• The earlier a disease is diagnosed and treated, it is better for prognosis and
prevention of the occurrence of further cases (secondary cases) or any
long-term disability.
• Not as effective and economical as "primary prevention"
• May be critically important in reducing the high morbidity and mortality in
certain diseases (essential hypertension, cancer cervix and breast cancer)
• For many others such as tuberculosis, leprosy and STI it is the only effective
mode of intervention

18. 4) Disability limitation
• When the patient reports late in the pathogenesis phase, the objective is to
prevent/halt the transition of the disease process from impairment to
handicap
i. Impairment: Any loss/abnormality of psychological, physiological or
anatomical structure or function. Eg-loss of foot/defective vision
ii. Disability: Inability or restiction to carry out certain activities in the
manner or within the range considered normal for the persons age sex
etc because of an impairment
iii. Handicap: disadvantage for a given individual, resulting from an
impairment or a disability, that limits or prevents the fulfilment of a role
expected of him in the society, that is normal (depending on age, sex,
and social and cultural factors) for that individual

19. Concept of disability
While impairment which is the earliest stage has a large medical component,
disability and handicap which are later stages have large social and
environmental components in terms of dependence and social cost

20. 5) Rehabilitation
• 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
• Includes all measures aimed at reducing the impact of disabling and
handicapping conditions and enabling the disabled & handicapped to
achieve social integration
• The following areas of concern have been identified in rehabilitation:
a) Medical rehabilitation - restoration of function
b) Vocational rehabilitation - restoration of the capacity to earn a livelihood
c) Social rehabilitation - restoration of family and social relationships
d) Psychological - restoration of personal dignity and confidence.
• Eg : schools for visually impaired, provision of aids for physically disabled

21. Control of Communicable diseases
• COMMUNICABLE DISEASE
An illness due to a specific infectious agent or its toxic products capable of being
directly or indirectly transmitted from man to man, animal to animal, or from the
environment (through air, dust, soil, water, food, etc.) to man or animal
• The term "disease control" describes (ongoing) operations aimed at reducing the:
i. incidence of disease
ii. duration of disease, and consequently the risk of transmission
iii. effects of infection, including both the physical and psychosocial
complications; and
iv. financial burden to the community
• Control activities may focus on primary prevention or secondary prevention, most
control programs combine the two

22. Control of Communicable diseases…
• Disease control: the disease "agent" is permitted to persist in the
community at a level where it ceases to be a public health problem
according to the tolerance of the local population
• Disease eradication: "tear out by roots"
- implies termination of all transmission of infection by extermination
of the infectious agent
- an absolute process, not a relative goal (all or none phenomenon)
- Word is reserved to cessation of infection & disease from whole world
- Smallpox; candidates for global eradication-polio, measles &
dracunculiasis

23. Control of Communicable diseases…
• Criteria for eradication:
1) There must not be any extra human reservoir
2) The incubation period should be short
3) Effective vaccine should be available
• Disease elimination:
- Interruption of transmission of disease; for example, elimination of
measles, polio and diphtheria from large geographic regions or areas
- Between control and eradication, an intermediate goal has been
described, called "regional elimination“
- Regional elimination is now seen as an important precursor of
eradication

24. Control of Communicable diseases…

25. Control of Communicable diseases…
• The basic approach is to identify weak points susceptible to attack for
every disease and break the weakest links in the chain of
transmission.
• This requires sound epidemiological knowledge of the disease - its
magnitude, distribution in time, place and person, multifactorial
causation, sources of infection and dynamics of transmission
• Removal/elimination of a single known essential link or the weakest
link may be sufficient to control a disease, even if complete
knowledge about the aetiology of the disease in question is lacking
(example - John Snow controlling the cholera epidemic in London by
removing the handle of the incriminated water pump)

26. Control of Communicable diseases…
• Disease control involves all the measures designed to prevent or
reduce as much as possible the incidence, prevalence and
consequences of diseases
• The activities of disease prevention and control are now included in
primary health care that includes community participation
(involvement), political support and inter-sectoral co-ordination
• Control measures for communicable diseases:
1) The reservoir or source of infection
2) The route(s) of transmission
3) The susceptible host (people at risk).

27. 1) Controlling the reservoir
• General measures of reservoir control in humans are all directed to
reduce the quantity of the agent available for dissemination
1. EARLY DIAGNOSIS
2. NOTIFICATION
3. EPIDEMIOLOGICAL INVESTIGATIONS
4. ISOLATION
5. TREATMENT
6. QUARANTINE

28. International Health Regulations (IHR)
• Health administrations are required to notify to WHO, Geneva of
occurrence of any communicable diseases under international
surveillance and International Health Regulations.
• Certain prescribed diseases are notified by the national health
authority to WHO which is mandatory
• These can be divided into:
a) Diseases subject to International Health Regulations (1969),
Third Annotated Edition, 1983 - cholera, plague and yellow
fever.
b) Diseases under surveillance (WHO) - louse-borne typhus fever,
relapsing fever, paralytic polio, malaria, viral influenza, etc.

29. 2) Interruption of transmission
• A major aspect of communicable disease control relates to "breaking
the chain of transmission" or interruption of transmission
• This may mean changing some components of human environment to
prevent the infective agent from a patient or carrier from entering the
body of susceptible person
• Blocking the routes of transmission imply an attack on environmental
factors, to bring about an adjusted equilibrium between host and
environment, through encouraging some ecological influences and
inhibiting others

30. 3) The susceptible host
• One effective way of controlling the spread of infection is to strengthen the
host defenses
I. ACTIVE IMMUNIZATION
• One of the most powerful and cost-effective weapons of modern medicine.
• A well thought-out immunization schedule must be
a) epidemiologically relevant: vaccinations should include diseases which
are public health problems and against which effective vaccine exists
b) immunologically effective: children must be vaccinated at an age when
they can benefit from it, i.e., when they are capable of forming defenses
and have lost the antibodies transmitted by the mother, before exposure
to possible infection

31. 3) The susceptible host…
c) operationally feasible: includes cost and ability to achieve a high percentage of
coverage which is the key factor in an effective immunization program that
minimizes the visit numbers by simultaneous administration of vaccines, and
d) socially acceptable: the schedule must take into account the local customs,
beliefs and practices, seasonal and climatic factors and daily work pattern of
the community including preventing long waiting time for patients whose sole
purpose of visit was to be immunized
II. PASSIVE IMMUNIZATION
• short-term measure useful only when exposure to infection has just
occurred or is imminent within a few days
• has a limited value in the mass control of disease but is recommended for
non-immune persons under special circumstance

32. 3) The susceptible host…
III. COMBINED PASSIVE AND ACTIVE IMMUNIZATION (Hep B)
IV. CHEMOPROPHYLAXIS - implies the protection from, or prevention of
disease
a) Causal prophylaxis implies the complete prevention of infection by the
early elimination of the invading or migrating causal agent.
- For example, there is no causal prophylaxis available against malaria.
b) Clinical prophylaxis implies the prevention of clinical symptoms; it does
not necessarily mean elimination of infection.

33. 3) The susceptible host…
V. NON SPECIFIC MEASURES
• Improvements in the quality of life (e.g., better housing, water supply,
sanitation, nutrition, education) fall into this category.
• Non-specific measures also includes "legislative measures", wherever
needed, to formulate integrated program and permit effective program
implementation
• Another important non-specific measure is community involvement in
disease surveillance, disease control and other public health activities.