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# Levels of prevention

- Concept

Prevention acts before risk appears, before disease, before symptoms, after harm, and also against too much medicine.

Updated Nov 5, 2026

## Key points

- Primordial: acts on social and environmental conditions so that the risk factor never appears (policy, urban design, taxes).
- Primary: in healthy people, stops disease from starting (vaccination, seat belts, quitting smoking).
- Secondary: finds disease in its subclinical stage and treats it early (screening).
- Tertiary: in established disease, reduces complications and disability (rehabilitation, diabetic foot care).
- Quaternary: identifies patients at risk of overmedicalisation and protects them from tests or treatments that do not help them.

## What it is

The levels of prevention sort interventions by the point in natural history where they act. Primordial prevention stops risk factors from appearing; primary stops disease from starting; secondary finds and treats it early; tertiary limits its sequelae; quaternary protects the patient from unnecessary interventions. A classic exam question: name the level from an example.

## Worked example

- Data (made up): a municipality has 50 000 adults and plans a programme against type 2 diabetes.
- Primordial: a local bylaw creates cycle lanes and school areas free of sugary drinks for all 50 000.
- Primary: 8 000 adults with prediabetes join a diet and exercise programme so they do not progress to diabetes.
- Secondary: blood glucose is measured in 12 000 adults over 40; 600 have undiagnosed diabetes: 600 / 12 000 = 5 %.
- Tertiary: 2 500 people with known diabetes join foot care; amputations fall from 20 to 12 a year.
- Reduction: (20 − 12) / 20 = 0.40, that is, 40 % fewer amputations.
- Quaternary: 300 healthy people who asked for tests every few months stop receiving tests without an indication.
- Reading: one problem has one intervention per level; each targets a different group and is measured with its own number.

## The five levels with one example each

| Level | When it acts | Example |
| --- | --- | --- |
| Primordial | Before the risk factor exists | Public spaces for exercise, food labelling |
| Primary | Healthy person, before disease | HPV vaccine, wearing a helmet |
| Secondary | Subclinical disease | Cervical cytology or HPV testing, blood pressure checks |
| Tertiary | Established clinical disease | Cardiac rehabilitation, diabetic foot care |
| Quaternary | Person exposed to over-intervention | Not repeating imaging without an indication in a healthy patient |

## Markers

- Primordial
- Primary
- Secondary
- Tertiary
- Quaternary

## In practice

- In an exam question, first decide whether the person is healthy, ill without symptoms or ill with symptoms: that sets the level.
- Quaternary prevention is part of daily work: every test without an indication brings false positives, costs and anxiety.

## Common pitfalls

- Calling screening primary: screening looks for disease that already exists, so it is secondary.
- Mixing up primordial and primary: primordial prevents the risk factor; primary acts when the risk already exists.

## Memory aid

Before the risk, before the disease, before the symptom, after the damage, and a brake on excess: five moments, five levels.

## Test yourself

Think of the answer, then tap the question to see it.

## Which level of prevention is cervical cancer screening with cytology?

Secondary prevention: it finds lesions that already exist, before symptoms, so they can be treated early.

## Which level is HPV vaccination of healthy girls?

Primary prevention: it stops the infection and the disease from starting.

## What does quaternary prevention aim to do?

Protect patients from overmedicalisation: unnecessary tests or treatments that may harm more than they help.

## How do primordial and primary prevention differ?

Primordial prevention stops risk factors from appearing in the population; primary prevention acts on people already exposed to risk so they do not become ill.

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## Connections

## Related 5

- [Natural history of disease](https://durgical.com/en/epidemiology/natural-history-of-disease/)
- [Principles of screening](https://durgical.com/en/epidemiology/principles-of-screening/)
- [Overdiagnosis](https://durgical.com/en/epidemiology/overdiagnosis/)
- [Epidemiologic triad and chain of infection](https://durgical.com/en/epidemiology/epidemiologic-triad-and-chain-of-infection/)
- [Social determinants of health](https://durgical.com/en/epidemiology/social-determinants-of-health/)

## Related conditions 3

- [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/)
- [Diabetic foot](https://durgical.com/en/conditions/diabetic-foot/)
- [Cervical cancer](https://durgical.com/en/conditions/cervical-cancer/)

[← All of epidemiology](https://durgical.com/en/epidemiology/)

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](https://archive.cdc.gov/www_cdc_gov/csels/dsepd/ss1978/lesson1/section9.html) (Centers for Disease Control and Prevention, 2012); [Screening programmes: a short guide. Increase effectiveness, maximize benefits and minimize harm](https://www.who.int/europe/publications/i/item/9789289054782) (World Health Organization, Regional Office for Europe, 2020).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/epidemiology/levels-of-prevention/