Spectrum and natural history of disease is discussed in this slides

1. NATURAL HISTORY &
SPECTRUM OF
DISEASES
Dr A Adeniran MBBS, MPH, FMCPH
Consultant Public Health Physician
Lagos State University (College of Medicine)
Nigeria

2. Learning Objectives
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 of Disease

4. 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 of the disease in an individual
starting from the moment of exposure to
the causal agents till one of the possible
outcomes occurs.

5. • Induction : time to disease
initiation
• Incubation:– time to
symptoms (infectious disease)
• Latency: time to detection
(NCDs) or to infectiousness in
CD
Natural history Phenomena
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6. Natural history of disease
Susceptible
host
TIME
Incubation period
Death
Recovery
Exposure Onset
Latent
Infection
No infection
Clinical disease
Infectious

7. - Pre-pathogenesis phase
- Pathogenesis phase
The natural history of disease can be
divided into two stages

8. Agent
Host Environment
Pre-pathogenesis
period
Pathogenesis period
Advanced
disease
Convales
-cence
Early
pathogenesis
Early
disease
Disability
Death
Recovery
Chronic
state
Natural history of disease
Pathogenesis phase:
The pathogenesis phase is
divided into
Stage of subclinical disease
Stage of clinical disease
Stage of disability

9. 99
Natural history of disease

10. Define the Following and State their roles
in the natural history of diseases
• Infectivity
• Pathogenicity
• Virulence

11. 11
Natural history & Spectrum of disease

12. Susceptible
Host
Subclinical
Disease
Clinical
Disease
Outcome:
Stage of Recovery,
Complications,
Disability, or Death
Point of
Exposure
Screening
Onset of
symptoms
Diagnosis
sought
Natural History of Disease
Detectable subclinical disease

13. Importance of studying natural history of disease
• 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

15. Spectrum of Disease
The full range of manifestations of
a disease
e.g from precursor state, to
subclinical and mild cases, to
florid and very severe disease

16. 1616
Spectrum of 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.
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Natural History& Spectrum of Diseases
The outcome will
depend on the
interactions of host,
agent and
environmental
factors.
Why do we have
varying degrees of
severity or outcome?

17. 1717
Classification of diseases according to clinical severity
(spectrum of disease)

18. 1818
The relation of severity of illness to disease statistics.

19. 1919
The pyramid and iceberg of disease
1 Diseased, diagnosed & controlled
2 Diagnosed, uncontrolled
3 Undiagnosed or wrongly
diagnosed disease
4 Risk factors for disease
5 Free of risk factors
Diagnosed
disease
Undiagnosed or
wrongly diagnosed
disease

20. 2020
• 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.
Iceberg Phenomenon
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The risk is that persons with in-apparent or
undiagnosed infections may be able to transmit
infection to others

21. 2121
Implications of the concepts of natural history and
spectrum of disease
• 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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22. Summary

23. Questions