Queensland Government
Queensland Health
Health Professionals > Endoscope Reprocessing

1.1 Disease Transmission & Control

This module looks at how disease is transmitted and introduces the concepts of standard and additional precautions which are used to control the transmission of disease. The many microorganisms, which are important in endoscopy, are also covered.


After you have worked through this module you will be able to:

Transmission of Disease

The world is teeming with microorganisms, many of which are harmless to humans. To cause an infection pathogenic organisms need to gain access to a susceptible human body. The spread of infection requires three elements:

To prevent the spread of infection it is therefore necessary to eliminate at least one of these elements.

Infection elements

Source of infecting microorganisms
Some infections are caused by the microorganisms that are already present on or in the human body, which acts as a reservoir of infection. These are referred to as endogenous infections. Other infections are caused by microorganisms from the external environment and are called exogenous infections.

Organisms that cause exogenous infections usually have a preferred portal of entry such as the gastrointestinal and respiratory tracts. The intact skin and mucous membranes lining the respiratory, gastrointestinal and genitourinary tract provide a protective barrier against these organisms. If this barrier is damaged or penetrated then the organisms can potentially gain entry to the body. In most endoscopic procedures the endoscope only comes in contact with intact mucous membranes. However, in some procedures, for example when a biopsy is taken, the mucous membrane is damaged.

Transmission of microorganisms
To cause an infection, pathogens have to be transferred from a reservoir or source to a susceptible host. Transmission of most microorganisms usually occurs from person to person, known as horizontal transmission. Transmission from mother to fetus across the placenta is called vertical transmission.

Horizontal spread of organisms can occur by contact transmission, which involves direct or indirect contact with the reservoir or source.

Hand touching a wound

Hands on endoscope

Droplets from sneezing

Infectious agents can also be transmitted over a wide area to many people by a common vehicle such as food, air or water. Legionnaires' disease is typically transmitted in this way. If the bacteria are present in water they can be dispersed in a fine aerosol spray then carried by air currents over a wide area. Transmission of disease in this manner is referred to as airborne transmission.

Susceptible host
Whether or not a particular microorganism infects a person depends on the balance between the power of the organism to cause disease and the power of the body to resist it. A variety of circumstances may increase the risk of infection associated with endoscopy these include:

Preventing the spread of infection
To prevent infection associated with endoscopy a number of interventions are utilised to control the source of microorganisms, prevent their transmission and to minimise the risks associated with increased host susceptibility. These are:

A discussion of the use of antimicrobial prophylaxis is beyond the scope of this training package.

 For more information about antimicrobial prophylaxis see: Infection Control in Endoscopy.

We will look at immunisation in the Workplace Health and Safety module, and will discuss cleaning, disinfection and sterilisation in detail in the Sterilisation and Disinfection and Reprocessing modules.

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Last Updated: 29 August 2011
Last Reviewed: 29 August 2011