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Infectious Diseases: How Do You Break the Chain?

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With the global COVID-19 pandemic having a severe impact on all aspects of society and the health of people worldwide, it is now more important than ever to update your knowledge on the spread and containment of infectious diseases, and what you can do to help break the chain of infection and contain the spread.

What is an Infectious Disease?

Infectious diseases are caused by pathogenic organisms including viruses, bacteria, fungi and parasites. They may be transmitted by other people, animals (zoonotic diseases) or environmental sources (e.g. water) depending on the specific pathogen (Mayo Clinic 2019).

Infectious diseases differ from non-infectious diseases (noncommunicable diseases) such as deficiency diseases, hereditary diseases and physiological diseases, because rather than developing on their own, they are caused by organisms that are not naturally found in the body (AIDSinfo n.d.).

The symptoms and severity of infectious diseases vary greatly depending on the pathogen causing them (Mayo Clinic 2019).

The Body’s Response to Infection

infectious, diseaTypes of Pathogen


Bacteria are small, singular cells that are able to survive in a variety of environments - sometimes in extreme cold or heat - without a living host. Bacteria exist in the body naturally and are mostly harmless, but others can cause infections. Bacterial infections can usually be treated with antibiotics (Mayo Clinic 2017).

Common bacterial infections include (but are not limited to):

  • Ear infection;
  • Strep throat (group B strep);
  • Urinary tract infection; and
  • Whooping cough.

(Healthdirect 2018)


Viruses are even smaller than bacteria, and are not cells - instead they invade and multiply within the cells of a host. They can not survive without a living host (Mayo Clinic 2017; Healthdirect 2018).

Viral infections include (but are not limited to):

  • Chickenpox;
  • Common cold;
  • COVID-19;
  • Ebola virus disease;
  • Glandular fever;
  • Hepatitis A, B and C;
  • Influenza;
  • Measles;
  • Viral meningitis;
  • Norovirus;
  • Rabies;
  • Severe Acute Respiratory Syndrome (SARS); and
  • Zika virus.

(Queensland Health n.d.)


Fungi are single-celled or multicellular organisms that reproduce using spores. They include molds, yeasts and mushrooms (Biology Dictionary 2017).

There are millions of fungi species, most of which are harmless. Only a few hundred varieties can cause illness (CDC 2019).

Fungal infections include (but are not limited to):

  • Fungal nail infections;
  • Ringworm; and
  • Candida infection (thrush) of the mouth, nouse, esophagus or vagina.

(CDC 2019)


Parasites are organisms that live in or on another organism and feed on them. Their size varies, with some parasites large enough to be visible with the naked eye (Sepsis Alliance 2017).

Disease-causing parasites are separated into three main classes:

  • Protozoa are microscopic and single-celled. They are most commonly transmitted between humans through a fecal-oral route.
  • Helminths are parasitic worms that can generally be seen with the naked eye. They are also commonly transferred through a fecal-oral route.
  • Ectoparasites (e.g. mosquitoes, lice, fleas, ticks) are organisms that attach and burrow into the skin. They can cause disease by themselves, but some ectoparasites, such as mosquitoes, can be transmitters of other, more serious pathogens.
  • (CDC 2016; Ho 2019)

    Parasitic infections include (but are not limited to):

    • Hookworm;
    • Lice infestation (body, hair, head, public);
    • Malaria;
    • Pinworm;
    • Scabies; and
    • Tapeworm.

    (CDC 2018)

    How are Infections Transmitted?

    The series of events enabling infections to spread between organisms is known as the ‘chain of infection’. There are six steps or ‘links’ in the chain that continue to repeat, and breaking any of these links will allow the chain to be dismantled (RCNi 2016).

    The Chain of Infection:

    1. Infectious Agent

    The pathogen that causes the infection (NFID 2016).

    2. Reservoir

    The habitat where the infectious agent is living and multiplying. This can be a human, animal, object or environmental source such as water or soil (RCNi 2016; NFID 2016).

    3. Portal of Exit

    The means through which the infectious agent escapes from the reservoir. This can include bodily excretions, open wounds, aerosols and unclean objects (RCNi 2016; NFID 2016).

    4. Mode of transmission

    The way in which the infectious agent spreads from one place to another (RCNi 2016). Different infections use different modes of transmission.

    These modes include:

    • Droplet transmission - The infectious agent spreads through large respiratory droplets in the air, which are then breathed in by another person. These droplets are released when an infected person coughs, sneezes or talks, travelling a short distance (about one metre) before falling to the ground. They may also contaminate nearby surfaces. If an uninfected person makes contact with these contaminated surfaces and touches their eyes, nose or mouth, this may also result in transmission.

    • Airborne transmission - Similarly to droplet transmission, the infectious agent spreads through respiratory droplets from an infected person. However, these droplets are much smaller in size, meaning they can stay suspended in the air for a longer period of time and be dispersed by air currents. Consequently, the air of the room of someone who has an airborne infection may be contaminated.

    • Direct contact - The infectious agent is spread through direct contact with an infected person/animal or their bodily fluids. This can include:
      • Touching an infected person (skin-to-skin);
      • Coming into contact with the bodily fluids of an infected person through activities such as kissing, breastfeeding or sexual intercourse;
      • Bodily fluids from an infected person entering the bloodstream of an uninfected person (through needles or breaks in the skin); and
      • Being bitten or scratched by an infected animal, or touching their waste.

    • Indirect contact - An uninfected person makes physical contact with a contaminated surface. A common example of this is faecal-oral spread, where tiny amounts of faeces from an infected person’s hands contaminate another surface. An uninfected person makes contact with this surface and then touches their mouth, allowing the particles of faeces to enter their body.

    • Insect transmission - Parasites such as mosquitoes and ticks may be carriers (‘vectors’) for other disease-causing pathogens such as malaria.

    • Food transmission - Some infectious agents can contaminate food or water, resulting in infection when it is consumed.

    (SA Health n.d., 2019; Ministry of Health NZ 2017; Mayo Clinic 2019; Government of Nunavut n.d.)

    5. Portal of Entry

    The means through which the infectious agent enters the new host. Depending on the mode of transmission this can occur through:

    • Being breathed in;
    • Being swallowed;
    • Entering open wounds or cuts;
    • Entering the respiratory tract;
    • Entering the mucous membranes; and
    • Entering through medical instruments placed into the body.

    (RCNi 2016; NFID 2016)

    6. Susceptible Host

    An uninfected individual who is susceptible to developing an infection when the infectious agent enters their body. Depending on the individual and the invading pathogen, they may be able to fight off the infection (RCNi 2016). Those who are more susceptible include:

    • Very young children;
    • Older adults;
    • Immunocompromised people;
    • People who are ill;
    • People with a long-term health condition; and
    • People who are physically weak (e.g. due to malnutrition or dehydration).

    (RCNi 2016)

    Preventing Infection Transmission (Breaking the Chain)

    In order to manage and prevent the spread of infectious diseases, it is important to interrupt the chain of infection at any of the six links.

    The specific preventative measures used will depend on the pathogen and its mode of transmission, however the following list offers some suggested strategies for breaking the chain of infection at each link.

    (Note: Infectious agents may still be present even if preventative measures are taken. However, the more measures implemented, the easier it will be to interrupt links of the chain. Prevention is most effective when a combination of measures are used.)

  • Infectious agent
    • Diagnosis and treatment; and
    • Antimicrobial stewardship.

  • Reservoir
    • Cleaning, disinfection and sterilisation;
    • Infection prevention policies; and
    • Pest control.

  • Portal of exit
    • Hand hygiene;
    • PPE;
    • Control of aerosols and splatter;
    • Respiratory etiquette; and
    • Waste disposal.

  • Mode of transmission
    • Hand hygiene;
    • PPE;
    • Food safety;
    • Cleaning, disinfection and sterilisation; and
    • Isolation.

  • Portal of entry
    • Hand hygiene;
    • PPE;
    • Personal hygiene;
    • First aid; and
    • Removal of catheter and tubes.

  • Susceptible host
    • Immunisations;
    • Treatment of underlying conditions; and
    • Patient education.
  • (APIC 2016)

    Additional Resources
    • AIDSinfo n.d., Infectious Disease, AIDSinfo, viewed 2 April 2020, https://aidsinfo.nih.gov/understanding-hiv-aids/glossary/3585/infectious-disease
    • Association for Professionals in Infection Control and Epidemiology 2016, Chain of Infection fact sheet, http://professionals.site.apic.org/files/2016/09/Break-the-Chain-of-Infection.pdf
    • South Australia Health, Infection Control Management of Infectious Diseases Summary Table, https://www.sahealth.sa.gov.au/wps/wcm/connect/2425ea004fe339d1977bb703541ce8ed/Infection-control-management-of- infectious-diseases-v2.7-201912.pdf
    • Healthdirect, Differences Between Bacterial and Viral Infection, https://www.healthdirect.gov.au/bacterial-vs-viral-infection
    • Infection Control Basic Principles Course, https://www.ausmed.com.au/cpd/courses/infection-control-basic-principles
    • Infec tion Control Cleaning Course, https://www.ausmed.com.au/cpd/courses/infection-control-cleaning
    • Hand Hygiene Essentials Course, https://www.ausmed.com.au/cpd/courses/hand-hygiene-essentials
    • Gastroenteritis Outbreak Management In Aged Care, https://www.ausmed.com.au/cpd/articles/gastroenteritis-outbreak-management-in-aged-care
    • How to Keep Yourself Safe from Infection, https://www.ausmed.com.au/cpd/lecture/keep-yourself-safe-from-infection
    Multiple Choice Questions Q1. True or false? Bacteria need a living host to survive.
  • True
  • False
  • Q2. True or false? Breaking any link of the chain of infection will stop the spread of infection.
  • True
  • False
  • Q3. Which of the following is an example of indirect contact as a mode of transmission?
  • Kissing an infected person.
  • Bodily fluids from an infected person entering the bloodstream of an uninfected person.
  • Contact with a surface that is contaminated by an infectious agent.
  • Contact with the waste of an infected animal.
  • References
    • Association for Professionals in Infection Control and Epidemiology 2016, Break the Chain of Infection, Association for Professionals in Infection Control and Epidemiology, viewed 1 March 2020, http://professionals.site.apic.org/files/2016/09/Break-the-Chain-of-Infection.pdf
    • Biology Dictionary 2017, Fungi, Biology Dictionary, viewed 31 March 2020, https://biologydictionary.net/fungi/
    • Centers for Disease Control and Prevention 2016, About Parasites, Centers for Disease Control and Prevention, viewed 31 March 2020, https://www.cdc.gov/parasites/about.html
    • Centers for Disease Control and Prevention 2018, Alphabetical Index of Parasitic Diseases, Centers for Disease Control and Prevention, viewed 1 April 2020, https://www.cdc.gov/parasites/az/index.html
    • Centers for Disease Control and Prevention 2019, Fungal Diseases, Centers for Disease Control and Prevention, viewed 31 March 2020, https://www.cdc.gov/fungal/index.html
    • Government of Nunavut n.d., Modes of Transmission, Government of Nunavut, viewed 2 April 2020, https://www.gov.nu.ca/sites/default/files/files/4_%20Modes%20of%20Transmission%20-%20march%2 05%20-%20low%20res.pdf
    • Healthdirect 2018, Differences Between Bacterial and Viral Infection, Healthdirect, viewed 31 March 2020, https://www.healthdirect.gov.au/bacterial-vs-viral-infection
    • Ho, V 2019, ‘What are Parasites and How do They Make us Sick?’, The Conversation, 18 November, viewed 31 March 2020, https://theconversation.com/what-are-parasites-and-how-do-they-make-us-sick-121489
    • Mayo Clinic 2017, Bacterial vs. Viral Infections: How do They Differ?, Mayo Clinic, viewed 31 March 2020, https://www.mayoclinic.org/diseases-conditions/infectious-diseases/expert-answer s/infectious-disease/faq-20058098
    • Mayo Clinic 2019, Infectious Diseases, Mayo Clinic, viewed 31 March 2020, https://www.mayoclinic.org/diseases-conditions/infectious-diseases/symptoms-causes/syc-20351173
    • Ministry of Health New Zealand 2017, How Infectious Diseases Spread, Ministry of Health New Zealand, viewed 1 April 2020, https://www.health.govt.nz/your-health/healthy-living/environmental-health/infectious-disease-prevention-and -control/how-infectious-diseases-spread
    • National Foundation for Infectious Diseases 2016, Help Break the Chain of Infection, National Foundation for Infectious Diseases, viewed 1 April 2020, https://www.nfid.org/2016/10/18/help-break-the-chain-of-infection/
    • Queensland Health n.d., Viral Infections, Queensland Health, viewed 31 March 2020, http://conditions.health.qld.gov.au/HealthCondition/home/topic/14/217/viral-infections
    • R oyal College of Nursing UK 2016, Chain of Infection, Royal College of Nursing UK, viewed 1 April 2020, https://rcni.com/hosted-content/rcn/first-steps/chain-of-infection
    • Sepsis Alliance 2020, Parasitic Infections, Sepsis Alliance, viewed 31 March 2020, https://www.sepsis.org/sepsisand/parasitic-infections/
    • South Australia Health 2019, Infection Control Management of Infectious Diseases Summary Table, South Australia Health, viewed 1 April 2020, https://www.sahealth.sa.gov.au/wps/wcm/connect/2425ea004fe339d1977bb703541ce8ed/Infection-control-management-of-infectious-diseases- v2.7-201912.pdf
    • South Australia Health n.d., Infectious Diseases Spread, South Australia Health, viewed 1 April 2020, https://www.sahealth.sa.gov.au/wps/wcm/connect/public+content/sa+health+internet/health+topics/heal th+conditions+prevention+and+treatment/infectious+diseases/
      (A nswers: b, a, c) Author Ausmed Editorial Team

    Ausmed’s Editorial team is committed to providing high-quality and thoroughly researched content to our readers, free of any commercial bias or conflict of interest. All articles are developed in consultation with healthcare professionals and peer reviewed where necessary, undergoing a yearly review to ensure all healthcare information is kept up to date. See Educator Profile

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