NATURAL HISTORY OF DISEASE &
LEVELS OF PREVENTION
Dr ZUMAIRA SUALEH
Definition
• It refers to the progress of a
disease process in an individual
over time, in the absence of
intervention.
• It describes the course of the
disease in an individual starting
from the moment of exposure to
the causal agents till one of the
possible outcomes occurs.
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.
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“
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
IMPORTANCE OF STUDYING
THE NATURAL HISTORY OF
DISEASES
• Understanding the progress
from disease onset to final
end point (cure or death) is
important for
epidemiologists.
• Knowledge of the natural
history is necessary for the
prevention and control of
disease
IMPORTANCE OF
STUDYING THE NATURAL
HISTORY OF DISEASES
• The intervention early in the
course of the disease
(asymptomatic stage) is likely
to change the course of the
disease favorably
• Adjusting lead time & length
bias for proper implementation
of screening program
PUBLIC HEALTH ASPECTS OF
NATURAL HISTORY OF
DISEASE AND DISEASE
SEVERITY
• Persons with in-apparent or
undiagnosed infections can transmit
infections to others.
• Control measures must be directed
toward all infections capable of being
transmitted to others;
 both clinically apparent cases and
 those with in-apparent or undiagnosed
infections
THANKYOU
.