For environmental health professionals

1. NATURAL HISTORY OF DISEASE
AND PREVENTION.

2. Objectives
• Understand different stages of disease
development.
• Relate the above stages to phases of
prevention.

3. Natural History of disease
• This implies the progression of disease in the
absence of intervention.
• It is imperative to study natural history of
disease because preventive measures can be
put up by understanding how infection occurs
and how a disease progresses..

4. Natural history (progression) of
disease consists:-
1. Appropriate exposure or accumulation of
agent.
2. Incubation period or latency period
How much time from the start of disease
process until disease?
All diseases have defined period of time before
symptoms occur (subclinical disease).
Can be seconds, days months of years
depending on agent.

5. 3. Clinical disease
It can result in any of the following
 Recovery
 persistent(chronic)
 Disability
 Death
 Chronic carriers
In this phase / stage of disease progression:
There maybe no evidence of active infection or clinical
illness but can still infect others. Most famous was
typhoid mary.
4. Disability

6. Natural history of disease illustration.

8. • STAGE 1: susceptibility
• DESCRIPTION:
Risk factors which assist the development of disease
exist, but disease has not developed in other words the
groundwork has been laid by the presence of factors that
favor its occurrence.
• Examples
 Smoking
 Unvaccinated child is susceptible to measles

9. • STAGE 2: Pre-symptomatic disease (subclinical)
• DESCRIPTION
Changes have occurred to lead toward illness but disease is
not yet clinically detectable i.e pathological changes have
started to occur in the body. The disease can only be detected
through special tests since the signs and symptoms of the
diseases are not present.
• Examples:
 alveoli deterioration in smokers.
 Detection of antibodies against HIV in an apparently
healthy person
 Ova of intestinal parasite in the stool of apparently healthy
children.

10. • STAGE 3: Clinical disease
• DESCRIPTION:
Detectable signs and symptoms of disease exist. The clinical stage of different
diseases differs in duration, severity and outcome. The outcomes of this stage
may be recovery, disability of death.
• Examples:
 emphysema detected by pulmonary function test.
 Common cold has a short and mild clinical stage and almost everyone
recovers quickly.
 Polio has a severe clinical stage and many patients develop paralysis
becoming disabled for the rest of their lives
 Rabies has a relatively short but severe clinical stage almost always results
in death.
 Diabetes mellitus has a relatively longer clinical stage and eventually
results in death if the patient is not properly treated.

11. • STAGE 4: Disability
• DESCRIPTION:
Disease has progressed to the point of causing a residual
effect. Some diseases may leave the person disabled for a
short or longer duration. Still, other diseases will end in death.
Disability is limitation of a person’s activities including one’s
role as a parent , wage earner, etc.
• Examples:
 Person with COPD has difficulty in breathing.
 Trachoma may cause blindness
 Meningitis may result in blindness or deafness. Meningitis
may also result in death.

12. Biological characteristics of disease
• Biology
 Infectivity
The ability of an agent to cause infection in a susceptible
host.
Measured by % of exposed people who become ill.
 Pathogenicity
Ability of agent to induce disease.
Measured by % of infected persons who develop
clinically apparent disease.
 Virulence
Severity of disease after infection occurs.
Measured by case -fatality rate.

13. • Reservior
The habitat in which the agent normally lives,
grows and multiplies.
• Mode of transmission
How is the disease spread?
Direct contact, indirect contact (airborne,
vector borne)

14. Prevention
• A major goal of epidemiology is to identify
subgroups in the population who are at high
risk for disease, so that we can direct
preventive efforts to populations who are
most likely to benefit from any interventions
that are developed for the disease.

15. Levels of prevention
• Primary prevention
prevention of disease by controlling risk factors (
e.g. non smoking promotion)
• Secondary prevention
Reduction in the consequences of disease by early
diagnosis and treatment. ( e.g. cervical cancer
screening)
• Tertiary Prevention
Reduction in the complications of disease

16. Illustration of the natural history of
disease and points at which prevention
can be carried out.

17. Levels of Prevention
• Level: Primary
• Description: Promote general health and avoid
risk factors. Utilize protective measures to
prevent susceptibility and presymptomatic
disease.
• Examples:
stop smoking or choose not to start; avoid areas
where people are smoking.
Education about good nutrition , the importance
of regular exercise and the dangers of abuse of
alcohol and other drugs.

18. Education and legislation about proper
seatbelt and helmet use.
Immunization against infectious disease
Controlling potential hazards at home and in
the work place
Regular exams and screening tests to
monitor risk factors for illness.

19. • Level: Secondary
• Description: early detection and timely
treatment . In other words, interventions
happen after an illness or serious risk factors
have already been diagnosed. The goal is to
halt or slow the progress of disease (if
possible) in its earliest stages; in the case of
injury, goals include limiting long-term
disability and preventing re-injury.

20. • Examples:
Routine pulmonary function tests for those at
risk; medicine to help patients breath more
easily; smoking cessation programs if patient
smokes.
Providing suitably modified work for injured
workers.
Recommending regular exams and screening
tests in people with known risk factors for illness.
Taking daily, low dose aspirin to prevent a first or
second heart attack or stroke for those at risk.

21. • Level: Tertiary
• Description: Focuses on helping people manage
complicated, long term health problems such as
diabetes, heart disease, cancer and chronic
musculoskeletal pain. The goals include
preventing further physical deterioration and
maximizing quality of life.
• Examples:
Cardiac of stroke rehabilitation programs
Chronic pain management programs
Patient support groups.

22. Oxygen therapy; facilitating ambulation with
technical devices.

23. Discussion questions.
• What level of prevention is:
1. HPV vaccination for cervical cancer?
2. Male Circumcision?

24. PREVENTION APPROACHES
• There are two approaches:
1. Population-Based Approach
2. High-Risk Approach

25. Population-Based approach
• Preventive measure widely applied to an
entire population
• Strives for small absolute change among many
persons.
• Must be relatively inexpensive and non
invasive.

26. High risk approach
• Target group: individuals at high risk.
• Strives for strong risk factor control
• Often times requires clinical action to identify
the high risk group and to motivate risk factor
control.

27. Quiz
• Write the primary, secondary and tertiary
prevention strategies for the diseases or
conditions listed in the table below
Disease primary secondary tertiary
A person lost
his leg in a car
accident
copd

28. THANKS!!!!
QUESTIONS