Natural history of disease
- Concept
The course a disease follows with no intervention: from a healthy, exposed person to symptoms and an outcome.
What it is
Natural history describes how a disease progresses in a person when nobody intervenes: susceptibility, subclinical stage, clinical stage and outcome (recovery, disability or death). Knowing it tells us when each level of prevention works and how useful it can be to find the disease before symptoms appear.
Worked example
- Data (made up): 1 000 adults aged 40 with normal blood pressure are followed for 10 years.
- Susceptibility: 400 of the 1 000 (40 %) are overweight or eat a lot of salt; primary prevention targets them.
- Subclinical stage: 150 people develop hypertension with no symptoms (150 / 1 000 = 15 %); only measuring finds it.
- A screening programme detects 120 of those 150: 120 / 150 = 80 % of subclinical cases.
- Clinical stage: 25 of the 150 with hypertension (≈ 17 %) have a stroke or a heart attack in those 10 years.
- Outcome of the 25: 6 recover fully, 15 are left with sequelae and 4 die (6 + 15 + 4 = 25).
- Tertiary prevention: the 15 with sequelae start rehabilitation to regain function and avoid a second event.
- Reading: each stage has its own group and number; acting earlier (on the 400 or the 150) keeps people from becoming the 25.
Stages of natural history and the level of prevention that acts in each
| Stage | What happens | Level of prevention | Example |
|---|---|---|---|
| Susceptibility | Exposure to risk factors, no disease | Primary | Vaccination, less salt in the diet |
| Subclinical | Pathological changes without symptoms | Secondary | Blood pressure screening or cervical cytology |
| Clinical | Symptoms and signs | Tertiary (and treatment) | Rehabilitation after a stroke |
| Outcome | Recovery, disability or death | Tertiary | Preventing relapses and complications |
Markers
- Susceptibility
- Subclinical
- Clinical
- Outcome
In practice
- Chronic diseases with a long, detectable subclinical stage (hypertension, cervical cancer) are good candidates for screening.
- In infections, carriers in the subclinical stage can transmit without knowing it, which matters for outbreak control.
Common pitfalls
- Mixing up the incubation period (infection) and the latency period (chronic disease): both are the subclinical stage.
- Assuming everyone goes through every stage: many people recover without reaching the clinical stage.
Test yourself
Think of the answer, then tap the question to see it.
At which stage of natural history does screening act?
At the subclinical stage: pathological changes are present but there are no symptoms yet.
What is the subclinical stage called in infectious and in chronic diseases?
The incubation period in infectious diseases and the latency period in chronic diseases.
What is the spectrum of a disease?
The range of forms it takes in a population, from silent infection or changes to severe or fatal cases.
Which level of prevention is rehabilitation after a heart attack?
Tertiary prevention: it reduces sequelae, disability and relapse in someone who already has the disease.
Connections
Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.
Sources: Principles of Epidemiology | Lesson 1 - Section 9 (Centers for Disease Control and Prevention, 2012); Screening programmes: a short guide. Increase effectiveness, maximize benefits and minimize harm (World Health Organization, Regional Office for Europe, 2020).
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Representative model, for educational purposes only.