Transcript Natural History of a disease

Natural History Of Diseases
and Levels of Prevention
By : Sourav Goswami
Moderator : Dr P R Deshmukh
Framework
• 1.Definition
• 2.Understanding Natural History of
Disease
• 3.Its Importance
• 4.Stages
• 5.Application : Levels of
Prevention/Screening/prognosis/E
valuation
Definition
• Natural History of a disease
signifies the way in which a
disease evolves over time from the
earliest stage of its
prepathogenesis phase to its
termination as recovery,disability
or death,in the absence of
treatment or prevention.
Natural history of disease
Natural history of Hepatitis B infection
SUSCEPTIBLE
HOST
HCC
DEATH
ENTRY
OF HBV
ON
EXPOSURE
OUTCOME
CARRIER
C
I
R
R
H
O
S
I
S
DEVEL
-OP
HEP-B
Natural History of Typhoid
Entry of
S.typhi
Incubation
period
14 days
DEATH/
DISABILITY(carrie
-r)
Headach
e, Fever,
Peasoup
stool
Palpabl
-e
spleen
,Rash
COMPLICATIONS:
Hemorrhage
Perforation
Peritonities
Recovery
TIME
Death
Clinical disease
Infection
Susceptible
host
Recovery
No infection
Incubation period
Latent
Exposure
Non-infectious
Infectious
Onset
Infectious period
the time during which the host can infect another
susceptible host
•Non-infectious period
the period when the host’s ability to transmit
disease to other hosts ceases
•Incubation period
the time interval between invasion by an
infectious agent and appearance of the first sign
or symptom of the disease in question
Latent period
It is used in non-infectious diseases as the
equivalent of incubation period in infectious
disease
-”Period from disease initiation to disease detection”
Stages of Natural History of
Disease
The natural history of disease can be
divided into two stages :
1. Pre-pathogenesis phase
2. Pathogenesis phase
1. Pre-Pathogenesis Phase / Stage of
susceptibility
In this stage, the disease has not developed
but the ground has been laid by the presence
of factors that favor its occurrence, for eg :
1.Alcohol consumption for
Cirrhosis of liver
2.High Cholesterol, obesity, Type A personality:
Heart Disease
3.Smoking, Hypertension, High Cholesterol :
Stroke
4.Radiation, Smoking, Immune suppression:
Cancer
Pathogenesis phase
• 1. Asymptomatic (Early Pathogenesis)
phase
• 2. Early, Discernible Disease
• 3. Full-Blown (Classical) Disease
• 4. Termination - a) Complete Recovery
•
b) Chronic Disease
•
c) Life With Residual
Disability
•
d) Death
Why is it important to study
natural history of disease?
• 1. For prevention of disease
• 2.Adjusting lead time & length bias
for proper implementation of
screening program
• 2.Forecasting prognosis
• 3. Evaluation of intervention
Prevention
Levels of prevention
• In general, there are mainly three
major levels of prevention, depending
on the phase of the natural history of
the disease :
• 1. Primary prevention (also primordial
prevention )
• 2. Secondary prevention
• 3. Tertiary prevention
• Primary prevention seeks to prevent the
onset of specific diseases via risk reduction:
• (a) by altering behaviors /exposures that can
lead to disease,(eg : cessation of smoking ) or
• (b) by enhancing resistance to the effects of
exposure to a disease agent (eg : Vaccination
)
• It can be done by : (1) Health Promotion
(2) Specific protection
Health Promotion
• “The process of enabling people to
increase control over, and to improve
health” (WHO)
It is not directed against any particular disease,
but is intended to strengthen the host through a
variety of approaches :
• 1.Health education
• 2.Environmental modifications
• 3.Nutritional intervention
• 4.Lifestyle and behavioural changes
Contd……
1) HEALTH EDUCATION : Most cost effective
intervention. Now people have moved to behavior
change communication.
2) ENVIRONMENTAL MODIFICATION :
# provision of safe water
#Installation of sanitary latrines
#Control of insects & rodents etc
3)NUTRITIONAL INTERVENTIONS :
# Food distribution & nutritional
improvements of vulnarable groups ( viz. Mid-day
meal in schools ,Khichri on Anganwadi etc ) etc
4) LIFE STYLE & BEHAVIOURAL CHANGE :
# motivation for healthy lifestyle
Specific protection
• immunization to protect against
specific diseases
• fortification of foods with specific
nutrients (as salt with iodine),
• use of condoms to protect against
STDs,
• use of chemoprophylactic drugs to
protect against particular diseases
(as malaria, meningococcal
meningitis, etc)
#Primordial Prevention
• This is prevention of the emergence of
risk factors in countries or population
groups in which they haven't yet
appeared.
• By “individual and mass education”
• It addresses BROAD HEALTH
DETERMINANTS rather than preventing
personal exposure to risk factors, which is
the goal of primary prevention.
Contd ……
• Thus, outlawing alcohol in
certain countries/areas would
represent primordial
prevention, whereas
• a campaign against drinking
and would be an example of
primary prevention.
Secondary prevention
• It include all actions undertaken at the
stage of early pathogenesis so as to halt
the progress of disease at it’s earliest
stage,
• It is done by “early diagnosis and
prompt treatment”
• eg : Screening for Cancer/ treatment of
Tuberculosis-early diagnosis & prompt
treatment/Diagnosis & treatment of
malaria
Tertiary Prevention
• It signifies interventions done in the late
pathogenesis phase.
• “All measures available to reduce or limit
impairments and disabilities,minimise
sufferings caused be existing departures from
good health and to promote the patient’s
adjustment to irremediable conditions” (
Last,, A Dictionary of Epidemiology )
• It can be attained by : a) Disability limitation
& b) Rehabilitation
Disability limitation
(impairment/disability/handicap)
• Impairment is defined as "any loss or
abnormality of psychological,
physiological, or anatomical
structure or function."
• Impairment is a deviation from
normal organ function; it may be
visible or invisible (screening tests
generally seek to identify
impairments).
• Disability is defined as "any restriction or lack
(resulting from an impairment) of ability to
perform an activity in the manner or within
the range considered normal for a human
being."
• An impairment does not necessarily lead to a
disability, for the impairment may be
corrected.
• For example, I am wearing eye glasses, but do
not perceive that any disability arises from my
impaired vision. A disability refers to the
function of the individual (rather than of an
organ, as with impairment).
• Handicap is defined as "a disadvantage for
a given individual, resulting from an
impairment or a disability, that limits or
prevents the fulfillment of a role that is
normal (depending on age, sex, and social
and cultural factors) for that individual."
• Handicap considers the person's participation
in their social context.
• For example, if there is a wheel-chair
access ramp at work, a disabled person
may not be handicapped in coming to work
there
Disability limitation
• Concept of disability:
DISEASE
Accident
(1)
DISABILITY
Cannot
walk
(3)
IMPAIRMENT
Loss of foot
(2)
HANDICAP
Unemployed
(4)
Contd…
• Disability limitation includes all measures
to prevent the occurrence of further
complications, impairments, disabilities
and handicaps or even death. For example
:
• When we apply plaster cast to a patient
who has suffered Colle’s fracture, we are
actually trying to prevent complications
and further disability like mal-union or
non-union (4)
Rehabilitation
• “Rehabilitation” (Re =restore into, habitat
= the original home or environment of
the person)
• “The combined and coordinated use of
medical,social,educational and vocational
measures for training and retraining the
individual to the highest possible level of
functional ability”
• It includes Physiotherapy,speech
therapy,audiology,psychology, vocational
work etc
Rehabilitation contd…
• The following areas of concern have been
identified :
• 1)Medical rehabilitation – restoration of
function
• 2)Vocational rehabilitation- restoration of
the capacity to earn a livelihood
• 3)Social rehabilitation –restoration of
family & social relationships
• 4)Psychological rehabilitation –
restoration of personal dignity and
confidence
Examples of rehabilitation
• Establishing schools for the blind,
• provision of aids for the crippled,
• reconstructive surgery in leprosy,
• change of profession for a more
suitable one etc
Knowledge of Natural
History of disease helps in
adjusting lead-time &
length bias…..which helps
in implementing proper
screening measures
HOW SCREENING WORKS
Pathology
Begins
Symptom
appears
X
DEATH
/
DISABI
LITY
SCREENING TEST &
EARLY DIAGNOSIS
(pre-symptom)
Concept of lead time
Pre
Detectable
AGE
20
Detectable
Pre-Clinical
30
Clinical
40
50
LEAD TIME
Possible
detection
by
Screening
Clinical
detection
Disabilit
y
Death
60
Survival time after diagnosis >
lead time
Length-time Bias
Aggressive Disease
Onset
6 mo.asymt
period
Screening interval
Clinical
1 yr sympto
Death
Presentation
1 year
Onset
Clinical
2 year asym
period
Presentation4 yr sym
Less Aggressive Disease
Death
How do we conclude – the
screening program is effective?
• We need to know the natural history
of the disease
• for evaluating the Lead time & Length
time bias
Prognosis: How much time do I
have doc???
•Prognosis is the
prediction of the course of
a disease
and
• is expressed as the
probability that a
particular event will occur
in the future
Prognosis contd …..
• Predictions are based on defined groups of
patients and the outcome may be quite
different for the individual patients
• However, knowledge of the likely prognosis is
helpful in determining the most useful
treatment.
• Prognostic factors are characteristics associated
with outcome in patients with the disease in
question.
• For example, for a patient with AMI, the
prognosis is directly related to heart muscle
function.
Rates commonly used to describe Prognosis
Rate
Definition
5 year survival
Percent of patients surviving 5 years from
some point in the course of disease
Case fatality
Percent of patients with a disease who die
of it
Disease-specific Number of people per 10,000 (or 100,000)
mortality
population dying of specific disease
Response
Percent of patients showing some evidence
of improvement following an intervention
Remission
Percent of patients entering a phase in
which disease is no longer detectable
Recurrence
Percent of patients who have return of
Application of natural history of disease :
Evaluation of interventional measures
Evaluation helps in
1)Providing feedback on the
effectiveness of a program
2)helps to determine whether the
program is appropriate for the target
population
•
• 3) is there any problems with its
implementation and support, and
• 4)whether there are any ongoing
concerns that need to be resolved as
the programme is implemented.
• 5)It helps in Comparing intervention
modalities
Reference
• 1) AFMC (Association of Faculties of Medicine of
Canada) Primer on Population Health-A virtual
textbook on Public Health concepts for
clinicians
• 2)Epidemiology by Leon Gordis( Fifth Edition)
• 3)Park’s testbook of Preventive and social
Medicine( 23rd edition )
• 4)Text book of Public Health and community
medicine by Armed Force Medical College
Thank you !