CATEGORIZATION AND CLASSIFICATION OF HEALTH STATES Nigel Paneth

HUMAN HEALTH STATES REALM OF PUBLIC HEALTH 1. DEATH 2. DISEASE 3. DISABILITY 4. DESTITUTION REALM OF POSSIBLE BIOLOGICAL HAZARD 5. DYSFUNCTION 6. DISCOMFORT A seventh state is DISSATISFACTION - sometimes of public health significance

HEALTH STATES OF PUBLIC HEALTH IMPORTANCE 1. DEATH -Not whether, but when. 2. DISEASE - A cluster of signs, symptoms and laboratory findings linked by a common patho- physiologic sequence, and that cause human distress. 3. DISABILITY and HANDICAP - Difficulty in performing expected functions, especially those important to ordinary human life, i.e. interfering with work, activities of daily living, etc. 4. DESTITUTION - The economic burden imposed by a health state.

Human health states perhaps indicative of a biological effect, but which do not, in themselves, constitute public health entities 5. DYSFUNCTION - Poor or subnormal performance on a test of some single or complex biological function. 6. DISCOMFORT – Uncomfortable symptoms such as dizziness, nausea, fatigue, but short of a specific disease.

THREE WAYS OF EXPRESSING HUMAN ILL-HEALTH DISEASE ILLNESS SICKNESS

DISEASE A cluster of signs, symptoms and laboratory findings linked by a common patho-physiologic sequence. Most epidemiology is about disease. ILLNESS The subjective state of the individual who feels aware of not being well. The ill individual may or may not be suffering from disease. SICKNESS The social role assumed by an individual suffering from an illness.

OTHER TERMS FOR ILL-HEALTH When the signs and symptoms have not yet clearly been placed in a common pathophysiologic sequence the disease is referred to as a SYNDROME. Diseases of a chronic nature are sometimes called CONDITIONS, especially if they are present since birth (although this distinction between disease and condition is not always emphasized, and the terms are often used interchangeably).

SPECTRUM OF DISEASE The point at which disease comes to medical attention may be anywhere along a SPECTRUM. Characteristically, population-based studies see a BROADER SPECTRUM OF DISEASE than do studies based on cases diagnosed in medical settings. This is important when we consider sampling next.

SPECTRUM OF DISEASE 1. EXPOSURE 2. SUBCLINICAL PATHOLOGIC CHANGES (in apparent infection especially important) 3. FIRST SYMPTOMS OR SIGNS/MILD DISEASE (usually diagnosed in outpatient setting) 4. MORE SEVERE DISEASE (may first be diagnosed in in-patient setting) 5. DEATH OR RECOVERY

Diseases are usually classified either by clinical manifestations or by etiology CLASSIFICATIONDATA USEDEXAMPLE MANIFESTATIONAL (or CLINICAL) signs/symptom s linked by common pathology Stroke Heart Attack Cancer ETIOLOGICALPresumed cause Fetal Alcohol Syndrome Lead Poisoning

Manifestation classifications are often more useful for treatment and management. Etiologic classifications are more useful for prevention.

FUNCTIONAL CLASSIFICATION OF HUMAN HEALTH STATES TYPE EXAMPLE NATURE OF INCAPACITY IMPAIRMENT Physical abnormality Arthritis DISABILITY (activity limitation) Inability to perform a human function Inability to use fingers for fine tasks HANDICAP (participation restriction) Inability to perform a social role Cannot work as a seamstress

Because epidemiology is interested in CASES OF DISEASE, it does not (usually) study the epidemiology of : symptom inventories abnormal laboratory tests health behaviors medical care

Major exceptions: where the test or behavior is closely linked to the disease, or a major risk factor for disease. Example 1 - SEROEPIDEMIOLOGY - the study of the prevalence of antibodies to a specific infectious agent. Example 2 - Hypertension, smoking, hypercholesterolemia

Epidemiology is often interested in biological phenomena with normal distributions. Examples: BLOOD PRESSURE BIRTH WEIGHT ADULT WEIGHT INTELLIGENCE QUOTIENT (IQ)

How is disease defined for such normally distributed measures? Because epidemiology is interested in cases of illness, it is generally more interested in TAILS OF THE DISTRIBUTION than in the entire distribution. Disease states are linked to the tails of the distribution of some normally distributed phenomena.

Epidemiology contrasted with other scientific approaches The physiologist studies blood pressure, the epidemiologist studies hypertension. The psychologist studies IQ, the epidemiologist studies mental retardation. The nutritionist studies adult weight, the epidemiologist studies obesity.