Download Disease Categorization and Classification

CATEGORIZATION AND
CLASSIFICATION OF HEALTH
STATES
Nigel Paneth
HUMAN HEALTH STATES
1. DEATH
REALM OF
PUBLIC
HEALTH
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 pathophysiologic 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
CLASSIFICATION
MANIFESTATIONAL
(or CLINICAL)
ETIOLOGICAL
DATA USED
signs/symptom
s linked by
common
pathology
Presumed
cause
EXAMPLE
Stroke
Heart Attack
Cancer
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
NATURE OF
INCAPACITY
EXAMPLE
IMPAIRMENT
Physical
abnormality
Arthritis
DISABILITY
(activity
limitation)
Inability to perform
a human function
Inability to
use fingers
for fine tasks
HANDICAP
Inability to perform Cannot work as
(participation a social role
a seamstress
restriction)
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.