The Chain of Infection

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In order for the spread of infectious diseases to take place the ‘chain of infection’ must be completed.

The first link in the chain is the causative agent. This is the harmful germ or pathogen that can cause infection, illness and disease, examples would include bacteria and viruses.

The second link is the reservoir or source. This is where pathogens live and multiply.  This could be in or on a person or an animal. Some replicate in an environmental reservoir such as water or Soil.

The third link is the means of exit. This is how pathogens leave the source. For example, pathogens that live in the respiratory tract (the lungs, throat, etc.) can leave the body through the mouth or nose with saliva or mucus when coughing or sneezing. Other examples of means of exit are broken skin, mucous membranes such as the eyes, via the stomach and via the intestines and anus.

The mode of transmission is the fourth link in the chain. It refers to how the pathogen is passed on from one person to another. Contact transmission is the most common route of transmission of pathogens in a health and social care workplace. This can happen by direct (hands) or indirect contact (equipment). Pathogens such as those that cause influenza and chickenpox can stay in the air for a long time and can be breathed in by other people.

The fifth link is the portal of entry. This is the way that the pathogen enters the body of the potential host. Pathogens can enter the body by coming into contact with broken skin, being breathed in or eaten, coming into contact with the eyes, nose and mouth or, for example when needles or catheters are inserted.

The sixth and final link   
in the chain is a person at risk. A person at risk is the individual the pathogen moves to. The risk of a person becoming infected depends on factors such as their general health and the strength of their immune system (which is the body’s system for fighting germs and micro-organisms).

Preventing infection means breaking the links in the chain so that an infection cannot spread. Some links are easier to break than others. For example, it is easier to stop a pathogen from entering a person than it is to stop one leaving an infected person.

The steps taken to protect individuals and workers from infection are an important part of providing high-quality care and support. It is vital to remember that not everybody who carries harmful micro-organisms will be ill or show any symptoms, so you must work in ways that prevent infection at all times. Standard precautions are the actions that should be taken in EVERY situation to reduce the risk of infection. 

These include good hand hygiene, safe disposal of waste, safe management of laundry and the correct use of Personal Protective Equipment or PPE.