Chain of infection

In order for infection to occur several things have to happen.  This is often referred to as the Chain of Infection. The six links in the chain are:

  1. The Infectious Agent – or the microorganism which has the ability to cause disease.

  2. The Reservoir or source of infection where the microorganism can live and thrive. This may be a person, an animal, any object in the general environment, food or water.

  3. The Portal of Exit from the reservoir. This describes the way the microorganism leaves the reservoir. For example, in the case of a person with flu, this would include coughing and sneezing. In the case of someone with gastro-enteritis microorganisms would be transmitted in the faeces or vomit.

  4. The Mode of Transmission. This describes how microorganisms are transmitted from one person or place to another. This could be via someone’s hands, on an object, through the air or bodily fluid contact.

  5. The Portal of Entry. This is how the infection enters another individual. This could be landing on a mucous membrane, being breathed in, entering via a wound, or a tube such as a catheter.

  6. The Susceptible Host. This describes the person who is vulnerable to infection.

Infection can be prevented by breaking the Chain of Infection.

The chain of infection diagram illustrates and gives examples of actions that can be taken to break it. The overall aim of Standard Infection Control Precautions (SICPs),  is to break the Chain.

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Chain of infection diagram alt text
This diagram shows the 6 different links of the chain of infection.  A diagram showing 6 links of a chain interlinked is in the middle of the diagram with the 6 boxes around it. Here is the description of the 6 boxes. 
Infectious agent: This is the microorganism or bug that can cause harmful infections and make you ill.  Common infections in care homes are respiratory such as cold and flu and stomach bugs like norovirus and clostridiodes difficile (C.diff) 
Reservoir: This is where the germ lives and grows.  This can be on a person for example in their respiratory tract or equipment, environment or on food and water.,
Portal of exit.  Way out: The germ then needs to find a way out of the infected person and then to spread. Ways out can be from sickness and diarrhoea and through the nose and mouth from coughing and sneezing. 
Mode of transmission:  Once the germ is out it can spread from one person to another by hands or on equipment such as a commode, in the air by coughing or contact with blood and body fluids.
Portal of entry. Way in: The germ then needs to find its way into another person.  This can be through the eyes or mouth, hands, open wounds or any tubes that go into the body such as a catheter or feeding tube. 
Susceptible host: This is the person who is at risk of infection as they are unable to fight the infection.  This could be residents, staff or visitors.  Elderly people can have a decreased immune system and catch infections easier. Infections also spread quickly in care homes due to many residents living together.