Download section 2 chain of infection

SECTION 2
CHAIN OF INFECTION
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Introduction
Infectious Agent
Reservoirs
Portal of Exit
Means of Transmission
Portal of Entry
Susceptible Host
Developed by
In conjunction with
Date developed
Approved by
Reference number
Revision date
Responsibility for
review
Niamh Mc Donnell, Liz Forde, Patricia Coughlan and Máire Flynn
-----------August 2012
Cork and Kerry Infection Prevention and Control Committee
Kerry Infection Prevention and Control Committee
IPCG 2/ 2012
Revision number
0
2015 or sooner if new evidence becomes available
Infection Prevention and Control Nurses
Guidelines on Infection Prevention and Control 2012
HSE South (Cork & Kerry)
Community and Disability Infection Control Services
Chain of Infection
Page 1 of 3
Introduction
The above diagram is used to explain the infection process and is referred to as
the chain of infection. All links in the chain must be present and in sequential order
for cross infection to occur. Understanding the characteristics of each link provides
the healthcare worker with methods to prevent the spread of healthcareassociated infection (HCAI).
The links are;
Infectious agent is a bug or micro-organism with the ability to cause disease.
The greater the micro-organism's virulence (ability to grow and multiply) and
pathogenicity (ability to cause disease), the greater the possibility that the microorganism will cause an infection. Infectious agents are bacteria, virus, fungi, and
parasites.
There are two sources of infection:
A. Endogenous or self infection: Occurs when organisms which are harmless in
one site cause infection when transferred to another (e.g. E. coli transferred
from the gastrointestinal tract to the urinary tract where it causes a urinary
tract infection).
B. Exogenous or cross infection: occurs when organisms are transferred from
another source (e.g. eating food contaminated with Salmonella species).
Reservoirs A place within which micro-organisms can thrive and reproduce. For
example, micro-organisms thrive in human beings, animals, and inanimate objects
such as water, on equipment and in the environment.
Portal of Exit A place of exit providing a way for a micro-organism to leave the
reservoir. For example, the microorganism (e.g. Flu) may leave the reservoir
through the nose or mouth when someone sneezes or coughs.
Means of Transmission In healthcare there are three main modes of
transmission,
 Contact (example via the hands of healthcare workers),
 Droplet (example flu) and
 Airborne (example TB) these are discussed in detail in section - transmission
based precautions.
Guidelines on Infection Prevention and Control 2012
HSE South (Cork & Kerry)
Community and Disability Infection Control Services
Chain of Infection
Page 2 of 3
Portal of Entry An opening allowing the micro-organism to enter the host. Portals
include body orifices, mucus membranes, or breaks in the skin. Portals also result
from tubes placed in body cavities, such as urinary catheters.
Susceptible Host A person who cannot resist a micro-organism invading the
body, multiplying, and resulting in infection. The host is susceptible to the disease,
lacking immunity or physical resistance to overcome the invasion by the
pathogenic micro-organism.
The purpose of Standard and Transmission-Based Precautions is to break
the “chain of infection” focusing primarily but not exclusively on the mode
of transmission, portal of entry and susceptible host sections of the chain.
References and Bibliography
Ayliffe, G AJ (2009) Control of Healthcare –associated Infection. Fifth Edition, Great Britain.
Centre for Disease Control and Healthcare Infection Control Practices Advisory Committee (2003) Guidelines for
Environmental Infection Control in Healthcare Facilities.
http://www.cdc.gov/hicpac/pdf/guidelines/eic_in_HCF_03.pdf
Infection Control for Nursing Students (2001) Chain of Infection http://faculty.ccc.edu/trinfectioncontrol/chain.htm
Guidelines on Infection Prevention and Control 2012
HSE South (Cork & Kerry)
Community and Disability Infection Control Services
Chain of Infection
Page 3 of 3