Levels of Prevention — Primordial, Primary, Secondary, Tertiary and Quaternary, with Modes of Intervention

Prevention means intervening to avoid disease and injury, and it can be applied at any point along the natural history of a disease. The classic framework of Leavell and Clark gave three levels — primary, secondary and tertiary — and five modes of intervention that sit inside them. Two levels were added later: primordial prevention (proposed by Strasser in 1978) at the very start, and quaternary prevention (proposed by Jamoulle) as an ethical check on medical care itself.

StatPearls describes five stages in the natural history of disease — underlying, susceptible, subclinical, clinical, and recovery/disability/death — and the preventive levels line up with them. Primordial prevention acts on the underlying stage, primary on the susceptible stage, secondary on the subclinical (preclinical) stage, and tertiary once clinical disease is established.

Primordial prevention consists of actions that minimise future hazards to health and so inhibit the establishment of risk factors in the first place. It addresses broad health determinants — social, economic, environmental and cultural — rather than an individual's exposure to a known risk factor, which is the job of primary prevention.

• Who proposed it: Strasser, in 1978 — the newest of the 'classic' four levels.
• Who delivers it: usually governments and institutions, through laws, taxes and national policy rather than one-to-one clinical care.
• Whom it targets: the whole population, and especially children, because it aims to prevent risk exposure as early as possible.
• Examples: taxing tobacco and restricting tobacco advertising; school education on diet and exercise; urban design (safe sidewalks, parks) that keeps obesity, hypertension and diabetes from developing.

Primary prevention acts in the prepathogenesis phase, before disease begins. It works either by changing behaviours or exposures that lead to disease, or by increasing resistance to a disease agent. It has two modes of intervention, and examiners love asking which mode a given action belongs to.

The WHO Community-Based Rehabilitation guidelines sum up primary prevention as interventions aimed at people (changing health behaviours, immunisation, nutrition) and at the environments they live in (safe water supplies, sanitation, good living and working conditions). StatPearls notes that combined lifestyle changes — diet, activity, not smoking and healthy weight — can cut coronary heart disease risk by more than 80%.

Secondary prevention detects and treats preclinical pathological changes to control the progression of disease. Its mode of intervention is early diagnosis and prompt treatment. Screening is often the first step, because intervening before symptoms appear is usually more effective and cheaper than waiting.

• Screening examples: mammography for breast cancer, cervical cytology (Pap smear) or HPV testing, blood pressure measurement, eye examinations to detect cataract.
• Early treatment examples (WHO CBR): antibiotics for trachoma to prevent blindness, multidrug therapy for leprosy to stop progression, correct handling of a fracture to prevent deformity.
• Community benefit: in communicable disease, early diagnosis and treatment of a case also cuts transmission to others — so case-finding and treating a sputum-positive TB patient is secondary prevention for that patient and protects the community.

Whether a condition is worth screening for is judged against the ten Wilson and Jungner principles (WHO, 1968). Key ones: the condition must be an important health problem; there must be an accepted treatment and facilities for diagnosis and treatment; there must be a recognisable latent or early symptomatic stage; the test must be suitable and acceptable; the natural history must be understood; and case-finding must be a continuing process, not a 'once and for all' project.

Once disease has developed and been treated in its acute phase, tertiary prevention aims to soften its impact on function, longevity and quality of life. It modifies the adverse consequences of established disease and restores function through physical, mental and social rehabilitation. Its two modes are disability limitation and rehabilitation.

Tertiary prevention can change prevalence in either direction. For reversible conditions it reduces prevalence; for incurable conditions it may increase prevalence because people survive longer with the disease. Where a condition is not reversible, the focus shifts to rehabilitation — helping the patient adapt to the disability.

Quaternary prevention was first proposed by Marc Jamoulle and M. Roland, presented to the WONCA classification committee in 1995. It is defined as action taken to identify a patient at risk of overmedicalisation, to protect him from new medical invasion, and to suggest interventions that are ethically acceptable. Its guiding principle is primum non nocere — first, do no harm.

• Problem it addresses: overscreening, overdiagnosis and overtreatment, which cause adverse effects, extra cost and anxiety.
• Examples: avoiding unnecessary imaging or invasive procedures in athletes; reconsidering intensive glycaemic control where trials showed no benefit or harm; resisting 'disease mongering' — the commercialisation of conditions.
• Where it acts: at every stage of care, as a safeguard laid over the other four levels — not as a separate stage of the natural history.

Leavell and Clark's five levels (modes) of preventive intervention are taught across medical schools: health promotion, specific protection, early diagnosis and prompt treatment, disability limitation and rehabilitation. Each belongs to one level of prevention.

Work out the disease status of the person at the moment of the intervention, not the disease's eventual outcome. Then match the action to its mode.

Geoffrey Rose's paper Sick individuals and sick populations (1985) described two complementary strategies for control. The high-risk approach seeks to protect susceptible individuals — for example, screening and treating people with very high blood pressure. The population approach seeks to control the causes of incidence across the whole population — for example, lowering salt intake for everyone.

• Rose argued that the two approaches are not usually in competition, but the prior concern should be to discover and control the causes of incidence.
• Population and primordial measures often look small for each person but shift the whole distribution of a risk factor — this is the basis of the prevention paradox.

1. Immunisation = primary prevention, specific protection — not health promotion.
2. Screening = secondary prevention, because disease is already present in a preclinical stage.
3. Primordial prevention prevents the risk factor; primary prevents the disease.
4. Disability limitation belongs with tertiary prevention alongside rehabilitation in the five-mode scheme.
5. Quaternary prevention protects against overmedicalisation — it means doing less, not more.
6. Primordial prevention was proposed by Strasser (1978); quaternary by Jamoulle; the three-level framework and five modes by Leavell and Clark.
7. Tertiary prevention of an incurable disease can raise its prevalence by prolonging survival.