Public Health Agency

Basic Principles


Infection prevention and control is the application of microbiology in clinical practice. Infection can be caused by bacteria, fungi, viruses or prions and can affect almost all body systems.

Not all infections are transmissible but some, such as Clostridium difficile, influenza and norovirus have the potential to spread from one patient to another. This has significant implications for healthcare organisations, facilities or nursing homes. Understanding how infections occur and how different micro-organisms spread is crucial to preventing infection.

Infection prevention and control is everyone’s responsibility and all healthcare workers have an important role to play. Healthcare-associated infections (HCAIs) can occur in any healthcare setting. While the specific risks may differ, the basic principles of infection prevention and control apply regardless of the setting. Although infections can spread easily, controlling the risk is relatively straightforward and simple measures can be effective. 

It is important that all members of staff have a clear understanding of their role in preventing the spread of infection. Staff should be familiar with the policies/guidelines and procedures that are in place to prevent and control infection and receive appropriate training and supervision. Records of Infection prevention & control training should be kept and used for updating and refresher courses should be considered. Courses should be mandatory and all staff, including nursing and medical staff, should attend.

The chain of infection

The process of infection can be represented as a chain, along which microorganisms are passed from a source to a vulnerable person.

Breaking a link at any point in the chain will control the risk of infection by preventing the onward transmission of microorganisms.

Opportunities to break the chain of infection

Transmission may be interrupted when:

  • The infectious agent is eliminated, inactivated or cannot survive in the reservoir (E.g. rapid identification and management of organisms, cleaning and disinfecting of the environment)
  • The portal of exit is managed through good infection prevention and control practices (E.g. Hand Hygiene, appropriate use of PPE, safe packaging and disposal of waste)
  • Transmission does not occur due to good infection prevention and control practices (E.g. Hand Hygiene, isolation of infected patients, air flow control where appropriate)
  • The portal of entry is protected (E.g. Aseptic non-touch technique, safe catheter care, wound care)
  • Reducing the susceptibility of patients receiving healthcare (E.g. Treatment of underlying disease, recognising high risk patients)

The difference between Colonisation and Infection


Colonisation is when microorganisms, including those that are pathogenic, are present at a body site (E.g. on the skin, mouth, intestines or airway) but are doing no harm and are not causing symptoms of infection. The person colonised is also called ‘a carrier’. For example, the skin is normally colonised by coagulase negative Staphylococci and can also be colonised by pathogenic Staphylococcus aureus. Colonisation occurs in some 30% of the population and whilst the microorganisms cause no harm if they remain on the skin, if transferred to another site e.g. a wound, or another person it can cause an infection.     


Infection is the process where an infectious agent (microorganism) invades and multiplies in the body tissues of the host resulting in the person developing clinical signs and symptoms of infection (E.g. Increased temperature, rigors, rash).   

Healthcare Associated Infection

Healthcare associated infections (HCAI’s) are infections that develop in a patient, as a direct result of receiving healthcare, either in hospital or in a community setting. The most commonly reported HCAI’s are urinary tract infections, wound infections and infections that cause vomiting and/or diarrhoea.