PRINCIPLES OF INFECTION

We live in harmony with millions of microbes that exist in the environment, on our skin and in our alimentary tracts and mucous membranes. Very few of these micro-organisms are pathogenic (cause disease) and infection will only occur if there is an imbalance between the environment, the human host and commensal (normal) microbes.

Individuals requiring surgery are particularly vulnerable to infection. In most cases, invasive surgery breaches the physical barriers to infection (skin and mucous membranes) and also causes stress to the body, both psychologically and physiologically. A high level of stress is known to suppress the immune system, thus increasing the likelihood of postoperative infection.

Endogenous (self-infection) infection occurs if microorganisms that normally exist harmlessly in one part of an individual's body transfer to another site on the same individual where they can become pathogenic. Exogenous (cross-infection) infections are caused by pathogens from a source other than an individual's own body. To prevent cross-infection in theatres, staff must be committed to the implementation of an infection control strategy that seeks to achieve three aims:

1. To control or remove the organism.

2. To eliminate methods of cross-infection.

3. To protect the population from infection.

THE CHAIN OF INFECTION

The series of components that must be present for infection to occur have been described as the chain of infection. There are five links in this ‘chain’:

1. Source of infection.

2. Reservoir.

3. Mode of transmission.

4. Individual at risk.

5. Portal of entry.

Infection control is based on disrupting or breaking one or more links in the chain.

SOURCES OF INFECTION

The invading organism or causative agent is a microbe that may be a bacterium, virus, fungus or parasite.

RESERVOIR

This is the environment in which the organism thrives. There are three important reservoirs of infection within the operating department:

1. Humans (staff, patients and others).

2. Environment.

3. Equipment.