class 1 of CTEEE

1. NATURAL HISTORY
&
SPECTRUM OF DISEASES
Spectrum : refers to Progression of desease

2. Implications of learning spectrum of disease
By the end of this lecture students will be able to:
• Describe natural history of diseases and their implications
for prevention of diseases.
• Describe spectrum of diseases and their implications for
on prevention of diseases.

3. Natural History ofDisease
Natural History of Disease: Natural course that a disease would take when it has
not been affected by any treatment or any other
intervention.
The natural history of a disease describes the course (progression) of the
disease in an individual starting from the moment of exposure to the
causative agents till one of the possible outcomes occurs.
•Infection/contract
•Induction : time to disease initiation
•Incubation:– time to symptoms (infectious disease)
•Latency: time to detection (NCDs) or to
infectiousness in CD
Natural historyPhenomena
- Pre-pathogenesis phase
- Pathogenesis phase
- Symptomatic / Clinical manifestation phase
Therefore, it is divided into two phases:

4. Natural history ofdisease: Time Course
TIME
Susceptible
host
Incubation period
Death
Recovery
Exposure Onset
Latent
Infection
No infection
Clinical disease
Infectious

5. 9
Natural history of disease
Morbidity & Mortality
• Infectivity & Pathogenicity
Virulence can occur at any stage of spectrum and
depends on the nature of individual pathogen and
respiratory pathogens spread fast.

6. 11
Natural history & Spectrum of disease

7. Spectrum ofDisease
• The full range of manifestations of a
disease
• e.g from precursor state, to
subclinical and mild cases, to florid
(collection of complete details) and
very severe disease
The concept that an exposure can lead to varying outcome:
signs, symptoms and severity of the same disease in the
population is the spectrum of disease.
Why do we have
varying degrees of
severity or outcome?
The outcome will depend on the
interactions of host, agent and
environmental factors.

8. Importance of studying natural history ofdisease
• Natural history is as important as causal understanding for
the prevention and control of disease.
• The earlier you can become aware of the disease the
more likely you will be able to intervene and save lives.
• Decides appropriate intervention at appropriate
stage of disease

9. Classification of diseases according to clinical severity
(spectrum of disease)
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(Qualitative representation only)
These are just examples & Other examples also can be tabulated
Inapparent Infection
The presence of infection in a host without occurrence of
recognizable clinical signs or symptoms.
Measles is an acute viral
respiratory illness. It is
characterized by a prodrome of
fever (as high as 105°F) and
malaise, cough, coryza, and
conjunctivitis -the three “C”s -,
a pathognomonic enanthema
(Koplik spots) followed by a
maculopapular rash. The rash
usually appears about 14 days
after a person is exposed.
Rabies is a deadly virus spread
to people from the saliva of
infected animals. The rabies
virus is usually transmitted
through a bite.
Severity Incidence
Severity
Incidence
Severity Incidence
Severity
Incidence

10. 18
The relation of severity of illness to disease statistics.
List of Examples can be tabulated ?

12. • Cases of illness correctly diagnosed by
clinicians in the community often represent only
the “tip of the iceberg.”
• Many additional cases may be too early to
diagnose or may remain asymptomatic.
• Examples: Tuberculosis, meningitis, polio,
hepatitis A, AIDS.
The risk is that persons with in-apparent or
undiagnosed infections may be able to transmit
infection to others
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Iceberg Phenomenon
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13. 21
Implicationsof the concepts of naturalhistoryand
spectrum ofdisease
• Persons with in-apparent or undiagnosed infections
can transmit infections to others.
• Control measures must be directed toward all
infections capable of being transmitted to others;
• both clinically apparent cases and
• those with in-apparent or undiagnosed infections.
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