The Chain of Infection

The chain of infection is a simple concept used to explain how a patient can acquire an infection from another person.

The Chain of Infection

The chain comprises of six sequential stages. If any of the links in the chain are missing then an infectious disease is unlikely to be transmitted to a new person.

Infection prevention and control protocols are developed from this basic concept.

By identifying the components that make up the chain of infection for a specific infection, then by breaking one or more of these links, transmission of the infection is stopped.

The components of the chain will vary depending on the microbe and the disease it causes.

It is used by epidemiologists and clinical microbiologists to develop strategies to prevent and control national epidemics such as pandemic flu.

This concept is also helpful when training staff in understanding infection control strategies used in the dental practice, or when conducting infection control risk assessments.

There are six components in the chain of infection and examples of each are shown in the diagram.

In the dental surgery transmission of infection occurs via the following routes:

Direct Contact

For example, transmission of microorganisms via contaminated hands, surfaces and instruments

Indirect Contact

For example, transmission via droplet spread contamination of dental surgery surfaces and instruments e.g. from the conventional speed handpiece, 3 in 1 and splatter of oral fluids during treatment

Aerosol Transmission

For example, aerolisation of oral microbes by rotary instruments; Aerosolisation of respiratory bacteria and viruses by coughing and sneezing

Common Source

For example, transmission from contaminated dental unit waterlines

Body Fluid Exposure Incidents

For example, percutaneous sharps injuries and splashing of the mucosa


All of these routes of transmitting infection can be controlled or eliminated if the appropriate procedures for disinfection, decontamination, waste and sharps management are followed and dental staff adhere to the correct usage of PPE (Personal Protective Equipment), use hand hygiene and receive occupational vaccines.