All about Infectious Disease epidemiology

1. Infectious Disease:
Epidemiology
Dr. Abdul Hadi

2.  Infection :
 The entry and development or multiplication of
an infectious agent in the body of man or
animals is called infection.
 It also implies that the body responds in some
way to defend itself against the invader, either in
the form of an immune response or disease.
 An infection does not always cause illness.

3.  Levels of infection :
a. Colonization - S. aureus in skin and normal
nasopharynx.
b. Subclinical or in apparent infection- Polio.
c. Latent infection - Virus of herpes simplex.
d. Manifest or clinical infection.

4.  Contamination :
 The presence of an infectious agent on a body surface; also on or in
clothes, beddings, toys, surgical instruments or dressings, or other
inanimate articles or substances including water, milk and food.
 Contamination on a body surface does not imply a carrier state.
 Pollution :
 Implies the presence of offensive, but not necessarily infectious matter
in the environment.
 Infestation :
 For persons or animals the lodgment, development and reproduction of
arthropods on the surface of the body or in the clothing, e.g. lice, itch
mite. Some authorities use the term for parasitic invasion of the gut.
e.g. ascariasis.

5.  Infectious disease :
 A clinically manifest disease of a man or animal resulting from an
infection.
 Contagious disease :
 A disease that is transmitted through contact. Example include
scabies, STD and leprosy.
 Communicable disease :
 An illness due to a specific infectious agent or its toxic product
capable of being directly or indirectly transmitted from man to
man, animal to animal, or from the environment through air,
dust, oil, water, food, etc. to man or animal.

6.  Epidemic :
 (Epi- upon, demos- people). The "unusual" occurrence of
disease, specific health related behavior (e.g. smoking) or
health related events (e.g. traffic accidents) in a community or
region clearly in excess of "expected occurrence ".
- Diarrhoeal disease.
 Endemic :
 (En-in, demos-people). It refers to the constant presence of a
disease or infectious agent within a defined area or population
group, without importing from outside.- Common cold.

7.  Sporadic :
 The word sporadic means scattered about. The cases occur irregularly,
haphazardly from time to time, and generally infrequently. - Meningitis.
 Pandemic :
 An epidemic usually affecting large proportion of the population,
occurring over a large geographic area such as a section of a nation,
the entire nation, a continent or the world. E.g. influenza pandemics of
1918 and 1962.
 Exotic :
 Diseases which are imported into a country in which they do not
otherwise occur, e.g. rabies in U.K. Ross River fever in Fizi.

8.  Zoonosis :
 An infection or infectious disease transmissible under natural
condition from vertebrate animals to man.- Rabies, anthrax.
 a. Anthropozoonosis :
 Infections transmitted to man from vertebrate animal.- rabies,
plague.
 b. Zooanthroponoses:
 Infections transmitted from man to vertebrate animals. – human
tuberculosis in cattle.
 c. amphixenoses :
 Infections maintained in both man and lower vertebrate animals that
may be in either directions. -T. cruzi, and S. japonicum.

9.  Nosocomial infection :
 Nosocomial (hospital acquired) infection is an infection
originating in a patient while in a hospital or other health care
facility.
 Opportunistic infection :
 This is infection by an organism that takes the opportunity
provided by a defect in host defense to infect the host and hence
cause disease.-Herpes simplex, cytomegalovirus, toxoplasma,
M.tuberculosis.
 Iatrogenic (physician-induced) disease :
 Any adverse consequence of a preventive, diagnostic or
therapeutic regimen or procedure, that causes impairment,
disability or death resulting from a physicians professional activity
or from the professional activity of other health professionals.

10.  Surveillance :
 The continuous scrutiny of the factors that determine the occurrence and
distribution of disease and other conditions of ill health.
 Eradication :
 Termination of transmission of infection by extermination of the infectious
agent through surveillance and containment.
 Eradication is an absolute process, an “all or none” phenomenon, restricted
to termination of an infection from the whole world.
 To-date only one disease has been eradicated, that is small pox.
 Elimination:
 The term elimination used to describe “eradication” of disease from a large
geographic region. E.g. Polio, Measles

11. THE CHAIN OF INFECTION
How diseases spread???

12. THE CHAIN OF INFECTION

14. How to prevent the
spread of Infection??

15. Breaking the chain of infection

17. MODES OF TRANSMISSION
Mode of transmission
Direct
transmission
Indirect
transmission
Direct contact
Droplet infection
Contact with soil
Inoculation into skin or mucosa
Trans-placental (vertical)
Vehicle-borne
Vector-borne:
Mechanical
biological
Air-borne
Fomite-born
Unclean hands
and fingers