In this section
Epidemiology is the study of disease transmission. The spread of
disease involves the following components:
All three components must be present for an infection to spread
from one person to another. This is what is called the 'chain
An organism may have a single route of transmission, or it may
be transmissible by two or more routes. If any one is missing, the
chain is broken and the potential for infection is eliminated.
Knowing the methods by which a disease is transmitted is
important in infection control and in attempting to decrease
nosocomial infections. It also demonstrates the importance for hand
hygiene in the 'chain of infection.'
The most common modes of transmission that occur in the hospital
environment are contact, droplet and airborne.
In contact spread, the susceptible person has contact with the
infected source or reservoir and the contact is either direct,
indirect or by droplets.
Airborne describes organisms have a true airborne phase in their
route of dissemination. This usually results in distance more than
several feet between the source and the victim.
Pathogens that are transmitted in this way are Varicella
(chicken pox) and tuberculosis (TB)
The 3rd link in the chain is the host or victim. Whether or not
the micororganism infects a person depends on the ability of the
organism to cause disease and the ability of the body to resist it.
Previous exposure and immune response will also play or role.
Disease does not always follow the transmission of
infectious agents to the host.
To prevent the spread of infection it is therefore necessary to
eliminate at least one of these elements.