What Is The Chain of Infection and How to Break it

Understanding how the infection is spread is essential to our efforts to prevent and contain its spread, especially when there is no definitive treatment available.

Modes of Transmission

There are three modes of transmission: contact, droplet, airborne.

Contact Transmission

Occurs when there is physical contact between an infected person/contaminated object and another person.
This can happen in two ways:

  1. Through direct contact where the infection travels to another person through touch.
  2. Through indirect contact when an individual touches an object contaminated by COVID-19.

When an infected person coughs, droplets can land on objects and surfaces around them. When another person touches these surfaces, their hands can get contaminated with the virus. If they touch their nose or mouth with contaminated hands, they can get infected. It is therefore essential to make hand hygiene a priority and wash your hands regularly.

Droplet Transmission

happens when an infected person coughs, sneezes, or talks, and tiny drops from the infected person enter another person’s eyes, nose and mouth.

Airborne Transmission

occurs when small particles in the air (<5um in size) containing the virus are inhaled into a person’s respiratory system (Pan et al., 2019). Although one study has reported that the virus can remain viable in the air for up to 3 hours (van Doremalen et al., 2020), more research is needed to confirm if airborne transmission occurs with COVID-19.

Chain of Infection

Certain conditions must be met in order for a microbe or infectious disease to be spread from person to person. This process is known as the chain of infection (CDC, 2016) which is shown in Fig 1. There are six steps in the chain of infection and transmission will only take place if all six links are intact.

  1. Infectious Agent – microorganism (e.g. virus, bacteria, or fungi)
  2. Reservoir (source) – a host which allows the microorganism to live, and possibly grow, and multiply. Humans, animals and the environment can all be reservoirs for microorganisms.
  3. Portal of Exit – a path for the microorganism to escape from the host. This can happen through the mouth, if a person coughs or sneezes, through a cut, if a person is bleeding, during diaper changes or toileting.
  4. Mode of Transmission – how the infectious agent is transmitted from one person to another. It can be in the form of droplets, direct or indirect contact, or through airborne transmission.
  5. Portal of Entry – a place for the microorganism to get into a new host, similar to the portal of exit.
  6. Susceptible Host – it’s either a baby, an elderly person or someone with a weakened immune system that is susceptible to the infectious agent.

If any of the links are broken then the infection will not occur. Infection Control principles are aimed at breaking one or more links in this chain.

Prevention Strategies

To prevent and of viruses, WHO recommends employing basic hygiene principles through standard and transmission-based precaution.

Standard precautions include:

  1. hand hygiene (5 Moments for Hand Hygiene);
  2. use of personal protective equipment (PPE)
  3. routine environment cleaning;
  4. cough etiquette
  5. aseptic technique

precautions include: use of appropriate personal protective equipment (PPE), including gloves, aprons or gowns, eyewear, face shields and face masks.

Hand Hygiene – 5 Moments of Hand Hygiene

1. BEFORE TOUCHING A PATIENTWhen: Clean hands before touching a patient when approaching him/her
Why: To protect the patient against harmful germs carried on your hands.
2. AFTER TOUCHING A PATIENTWhen: Clean your hands immediately before performing a clean/aseptic procedure. 
Why: To protect the patient agaisnt harmful germs, including the patient’s own, from entering his/her body. 
3. AFTER BODY EXPOSURE RISK When: Clean your hands immediately after an exposure risk to body fluids (and after glove removal). 
Why: To protect yourself and the health-care environment from harmful patient germs.
4. AFTER TOUCHING A PATIENTWhen: Clean your hands after touching a patient and her/his immediate surroundings, when leaving the patient’s side. 
Why: To protect yourself and the health-care environment from harmful patient germs.
5. AFTER TOUCHING PATIENT SURROUNDINGSWhen: Clean your hands after touching any object or furniture in the patient’s immediate surroundings, when leaving – even if the patient has not been touched. 
Why: To protect yourself and the health-care environment from harmful patient germs.

Washing Hands with Soap and Water Regularly

Hand washing thoroughly with soap and water is one of the best ways to prevent you or someone you know from getting infected. Washing your hands frequently helps to remove potentially harmful microorganisms from your hands which helps stop the spread of infection. The recommendations for washing your hands by following the 12 steps shown in the image below.

Using Hand Sanitiser

When you don’t have access to soap and water, using hand sanitiser containing at least 60% alcohol, such as PrimeOn Hand Sanitiser is a great way to ensure your hands are clean. Make sure to check the bottle’s label for the kill log rate to see how effective it is.

When using hand sanitiser, make sure to follow the steps below:

Cough and Sneeze Etiquette

As droplets from coughs and sneezes travel up to 2 metres, these simple steps can help to reduce the spread of COVID-19. Individuals with symptoms of acute respiratory infection should practise cough etiquette by maintaining distance with others. Where possible, close contact with people suffering from acute respiratory infections should be avoided.

  • Cover your mouth and nose with a tissue when coughing or sneezing and dispose of the tissue immediately
  • If you do not have a tissue, sneeze into your elbow rather than your hands.
  • Only when you are sick should you wear a face mask when out in public to prevent infecting others around you.
  • Wash your hands with soap and water immediately after coughing or sneezing.

Routine Environmental Cleaning

To break the chain and prevent infection, it is important to be more mindful about the surfaces we touch and to keep those surfaces clean. It is recommended to enhance the cleaning and disinfecting of a patient’s environment. Healthcare workers should wear gloves and PPE when in a patient’s surrounding and clean high-risk areas to prevent any potential spread of the infection.

  • clean and disinfect frequently used surfaces such as benchtops, desks and doorknobs
  • clean and disinfect frequently used objects such as mobile phones, keys, wallets and work passes
  • to increase the amount of fresh air available by opening windows or adjusting the conditioning.

(Source: Australian Government Department of Health)

Reference List

Pan, M., Lednicky, J. and Wu, C., 2019. Collection, particle sizing and detection of airborne viruses. Journal of Applied Microbiology, [online] 127(6), pp.1596-1611. Available at: <https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/jam.14278> [Accessed 24 April 2020].

Shaban, R., Sotomayor-Castillo, C., Radford, K., Bell, S. and Malik, J., 2020. COVID-19 And Breaking The Chain Of Infection. [online] Hospitalhealth.com.au. Available at: <https://www.hospitalhealth.com.au/content/clinical-services/article/covid-19-and-breaking-the-chain-of-infection-691528450#ixzz6K6ktlGun> [Accessed 21 April 2020]

. van Doremalen, N., Bushmaker, T., Morris, D., Holbrook, M., Gamble, A., Williamson, B., Tamin, A., Harcourt, J., Thornburg, N., Gerber, S., Lloyd-Smith, J., de Wit, E. and Munster, V., 2020. Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1. MedRXiV,

World Health Organization. Global Surveillance for human infection with the novel coronavirus (2019-nCoV). World Health Organization, 2020.