Natural history & spectrum of diseases
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Transcript of Natural history & spectrum of diseases
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NATURAL HISTORY & SPECTRUM OF DISEASESDr A Adeniran MBBS, MPH, FMCPH
Consultant Public Health PhysicianLagos State University (College of Medicine)Nigeria
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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.
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Natural History of Disease
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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.
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• 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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Natural history of disease
Susceptiblehost
TIME
Incubation period
Death
Recovery
Exposure Onset
Latent
Infection
No infection
Clinical disease
Infectious
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- Pre-pathogenesis phase- Pathogenesis phase
The natural history of disease can be divided into two stages
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Agent
Host Environment
Pre-pathogenesis period
Pathogenesis period
Advanced disease
Convales-cence
Early pathogenesis
Early disease
DisabilityDeathRecoveryChronic state
Natural history of disease
Pathogenesis phase:The pathogenesis phase is divided into Stage of subclinical disease Stage of clinical diseaseStage of disability
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Natural history of disease
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Define the Following and State their roles in the natural history of diseases
• Infectivity• Pathogenicity• Virulence
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Natural history & Spectrum of disease
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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 DiseaseDetectable subclinical disease
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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
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Spectrum of Disease
The full range of manifestations of a diseasee.g from precursor state, to subclinical and mild cases, to florid and very severe disease
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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?
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Classification of diseases according to clinical severity (spectrum of disease)
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The relation of severity of illness to disease statistics.
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The pyramid and iceberg of disease
1 Diseased, diagnosed & controlled
2 Diagnosed, uncontrolled
3 Undiagnosed or wronglydiagnosed disease
4 Risk factors for disease
5 Free of risk factors
Diagnosed disease
Undiagnosed orwrongly diagnosed disease
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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
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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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Summary
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Questions