of infectious disease
Epidemiology
اﻟﻣرﺣﻠﺔ اﻟراﺑﻌﺔ
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Infectious diseases are caused by pathogenic microorganisms, such as bacteria,
viruses, parasites or fungi; the diseases can be spread, directly or indirectly, from one
person to another. Zoonotic diseases are infectious diseases of animals that can cause
disease when transmitted to humans.
What is infectious disease epidemiology used for?
1- Identification of causes of new, emerging infections
-
2-Surveillence of infectious disease
3-Identification of source of outbreaks
5-Studies of routes of transmission and natural history of infections
6- Identification of new interventions
Epidemiology is the study of the distribution and determinants of health-related states
and events in populations, and the application of this study to control health problems.
Epidemiologic triad:
Host :Demographic characteristics , Biological characteristics and Socioeconomic
characteristics
Environment : Physical , social and Biological environment
Agent: Infectivity , Pathogenicity , Virulence ,Immunogenicity , Antigenic stability
and Survival
Terminology and Definitions:
& development or multiplication of an infectious agent in the
entry
: the
Infection
body of persons or animals
an organism (virus, rickettsia, bacteria, fungus, protozon or
Infectious agent:
helimentheses) that is capable of producing infection
expresses the ability of organism to enter, survive & multiply in the host
Infectivity:
also known as communicable diseases, contagious diseases or
:
Infectious disease
transmissible diseases comprise clinically evident illness (i.e., characteristic medical
signs and/or symptoms of disease). In certain cases, infectious diseases may be
asymptomatic for much or all of their course
in
The presence of an infectious agent on a body surface, on or
Contamination:
clothes, beddings, toys, surgical instruments or dressings, or other articles or
substances including water and food
the time interval between initial contact with an infectious agent
Incubation period:
& the first apparent of the symptoms associated with the infection.
a person or animal that has been in such association with an infected person
Contact:
or animal or a contaminated environment as to have an opportunity to acquire the
infection.
ty, population
(also called herd effect, community immuni
Herd immunity:
immunity, or social immunity) is a form of indirect protection from infectious disease
that occurs when a large percentage of a population has become immune to an
infection, thereby providing a measure of protection for individuals who are not
immune. In a population in which a large number of individuals are immune, chains
of infection are likely to be disrupted, which stops or slows the spread of disease. The
greater the proportion of individuals in a community who are immune, the smaller the
probability that those who are not immune will come into contact with an infectious
individual.
as applied to patients, isolation represent separation, for the period of
U
Isolation:
U
communicability, of infected persons or animals from others in such places & under
such conditions as to prevent or limit the direct or indirect transmission of the
infectious agents from those infected to those who are susceptible to infection or who
may spread the agent to others
s of well persons or animals that have been
restriction of the activitie
Quarantine:
exposed to a case of communicable disease during its period of communicability (i.e.
contacts) to prevent disease transmission during the incubation period if infection
should occur
to an infectious
lodgment
at affords subsistence or
A person or an animal th
Host:
agent under natural conditions.
(of infectious agents) any person, animal, arthropod, plant, soil or
Reservoir:
substance (or combination of these) in which an infectious agent normally lives &
multiplies, on which it depends primarily for survival, & where it reproduces it self in
such manner that it can be transmitted to a susceptible host
A case is defined as “a person in the population or study group identified as
Cases:
having the particular disease, health disorder, or condition under investigation
”
:Apparently healthy individual who is harboring virulent pathogenic
Carrier
organisms in his body & discharging them to outside his body into the environment to
infect others.
- They are more dangerous sources of infection than cases???
, Larger than cases in number
Move & mix easily
, Diagnosis is difficult
No measures or precautions
and Dangerous groups
Nosocomial (hospital acquired) infection is an infection
Nosocomial infections:
originating in a patient while in a hospital or another health care facility. It has to be a
new disorder unrelated to the patient’s primary condition. Examples include infection
of surgical wounds, hepatitis B and urinary tract infections.
This is infection by organisms that take the opportunity
nfection:
Opportunistic i
provided by a defect in host defense (e.g. immunity) to infect the host and thus cause
disease. For example, opportunistic infections are very common in AIDS. Organisms
include Herpes simplex, M. tuberculosis.
describes the mechanisms by which an infectious agent is
:
transmission
Mode of
skin: Herpes type 1
-
( Skin
:
direct
spread to human. Such mechanism include
, Across placenta : toxoplasmosis, breast milk:HIV
, Sneeze-cough : Influenza)
Hepatitis A,
borne:
-
Water
Salmonella,
borne:
-
Food
Chickenpox,
:
airborne
: (
ndirect
I
Vector-borne
Malaria:
is the time (days, weeks or months) during which an
Period of communicability:
infectious agent may be transmitted, directly or indirectly, from an infected person to
another person, from infected animals to humans, or from an infected person to
animal or arthropod
ures taken so as no new cases of such disease is allowed to occur
Meas
Prevention:
)
Incidence = zero
(
Measures designed to prevent or reduce as much as possible the incidence,
Control:
prevalence and consequences of disease
o the incidence of a specified disease in a
:Reduction to zer
Elimination of disease
defined geographical area as a result of deliberate efforts and Continued intervention
measures.
Reduction to zero of the incidence of infection caused by
:
Elimination of infections
a specific agent in a defined geographical area as a result of
deliberate efforts and
Continued measures to prevent
re-establishment of transmission.
Permanent reduction to zero of the worldwide incidence of infection
Eradication:
caused by a specific agent because of deliberate efforts So intervention measures are
no longer needed.
: number of new cases in a given time period
Incidence of an infectious disease
expressed as percent infected per year (cumulative incidence) or number per person
time of observation (incidence density)
expressed as a
(
number of cases at a given time
Prevalence of an infectious disease:
percent at a given time). Prevalence is a product of incidence x duration of disease,
and is of little interest if an infectious disease is of short duration (i.e. measles), but
may be of interest if an infectious disease is of long duration (i.e. chronic hepatitis B).
ommunity of disease, specific health related
The unusual occurrence in a c
Epidemic:
behavior, or other health related events clearly in excess of expected occurrence.
It is an
(
.
localized epidemic
,
: The term outbreak is used to describe small
Outbreak
epidemic in confined place) e.g: school , camp.
It refers to the constant presence of a disease or
(En = in; demos = people)
Endemic:
infectious agent within a given geographic area or population group. It is the usual or
expected frequency of disease within a population
The term “hyperendemic” expresses that the disease is constantly present at high
incidence and/or prevalence rate and affects all age groups equally.
The term “holoendemic” expresses a high level of infection beginning early in life
and affecting most of the child population, leading to a state of equilibrium such that
the adult population shows evidence of the disease much less commonly than do the
children (e.g. malaria)
An epidemic usually affecting a large proportion of the population,
Pandemic:
occurring over a wide geographic area such as a section of a nation, the entire nation,
a continent or the world, e.g. Influenza pandemics
are those which are imported into a country in which they do not
:
Exotic diseases
otherwise occur, as for example, rabies in the UK
The word sporadic means “scattered about”. The cases occur irregularly,
Sporadic:
haphazardly from time to time, and generally infrequently. The cases are few and
separated widely in time and place that they show no or little connection with each
other, nor a recognizable common source of infection e.g. polio, meningococcal
meningitis, tetanus
ividuals who become clinically
immune exposed ind
-
proportion of non
Attack rate:
ill (ill / exposed)
Primary (index)/secondary cases: The person who comes into and infects a
population is the primary case. Those who subsequently contract the infection are
secondary cases. Further spread is described as "waves" or "generations.
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