The Swiss Cheese Model: Understanding How We Prevent the Spread of Infection

Think about how many patients you might come into contact with during a shift. You could be helping one patient wash, taking observations from another, assisting with meals and then preparing someone for a procedure. Throughout the day, you move between patients, equipment and different areas of the ward.

During each activity, there are opportunities for microorganisms to spread. They may be transferred through contaminated hands or equipment, respiratory particles, food or contact with infected body fluids. How an infection spreads depends on the organism involved, which is why infection prevention involves more than one precaution.

The Swiss Cheese Model is a way of understanding why several protective measures are needed. It explains something you will see on every placement: one precaution might have a gap, but another may still prevent harm.

Why Swiss cheese?

Psychologist James Reason developed the model to explain how accidents can happen despite safety systems being in place. Imagine several slices of Swiss cheese standing one behind another. Each slice represents a protective measure; the holes represent weaknesses. If the gaps happen to line up, a hazard could pass through all the layers. If the gaps do not line up, a later layer may stop it.

Vaccination, hand hygiene, safe food handling and cleaning are four possible protective layers. They are not equally relevant to every infection. Food safety is particularly important for foodborne illness, for example, while influenza prevention calls for attention to respiratory precautions, vaccination, patient placement and the care environment.

Vaccination prepares the immune system to respond to particular infectious agents. Depending on the vaccine and disease, it can reduce the chance of infection, transmission or severe illness, but it does not provide complete protection. Hand hygiene helps interrupt transfer between people, equipment and surfaces, although hands can be contaminated again during care. Cleaning and decontamination reduce microorganisms on shared items and in the environment. Each layer addresses a different opportunity for infection to spread.

Think about the moments between tasks

On placement, hand hygiene should become part of the way you move through patient care, rather than something you do only when entering or leaving the ward. The World Health Organization's Five Moments for Hand Hygiene, used in NHSScotland guidance, help you recognise when it matters most.

Hand rub is appropriate for many routine care situations, but soap and water are required in particular circumstances, including when hands are visibly dirty, potentially contaminated with blood or body fluids, or following care involving vomiting, diarrhoea or a suspected gastrointestinal infection such as norovirus or Clostridioides difficile. The choice should follow current local and national infection prevention guidance.

If you want a closer look at why these actions work, the Bleepbook article Hand Hygiene: What Are You Actually Removing From Your Hands? explains what happens when microorganisms are removed from the skin.

How does it look on a real ward?

Imagine you are working on a medical ward where a patient has influenza. The patient is coughing and needs regular observations and help with personal care. Before you enter, you check which precautions are in place and gather the equipment you need. Assessing the infection risk and arranging appropriate placement form one layer. Task-appropriate personal protective equipment (PPE) forms another. Hand hygiene and correct decontamination of reusable equipment add further protection.

Now picture a blood pressure cuff moving from this patient to someone in the next bay. If it is not cleaned appropriately between uses, microorganisms may be transferred on its surface. Cleaning the cuff is one safeguard. Hand hygiene before and after patient contact, alongside other appropriate precautions, helps reduce the chance of onward spread.

This is the model in everyday practice. A single missed step increases risk, but other safeguards may still interrupt transmission. It also shows why infection prevention is not only about an individual's actions. An empty hand rub dispenser, unsuitable equipment or poor access to cleaning facilities can weaken the system. Healthcare organisations need to provide the resources, training and environment that make safe practice possible.

What does this mean for student nurses?

In Scotland, standard infection control precautions apply to all patients in all care settings, whether an infection is known or suspected. Additional transmission-based precautions are used when the assessed infection risk calls for them. You will learn to match those precautions to the care you are giving and the risks involved.

Consider helping a patient with personal care. You assess the task, perform hand hygiene, choose PPE according to the expected exposure, manage used linen safely, clean any reusable equipment and perform hand hygiene again at the appropriate point. The steps may become familiar, but they are doing different jobs. Together, they help prevent microorganisms travelling from one patient, surface or procedure to another.

The same principle applies beyond hospitals. Communities use several layers of protection through vaccination, clean water, sanitation, safe food preparation, ventilation and public health measures. The exact layers change with the setting and the disease.

Next time you are on placement, choose an everyday activity and ask yourself what each infection prevention action is achieving. That is where the model becomes useful: it helps you see the reason behind the precautions, rather than remembering a checklist without understanding it.

One layer may have weaknesses. The right layers working together reduce the risk of infection.

Further reading

NHSScotland National Infection Prevention and Control Manual: Standard Infection Control Precautions and Chapter 2: Transmission Based Precautions.