Education, Epidemiology, Infectious Diseases

What Is the Chain of Infection and How to Break It?

Author Chandana Balasubramanian , 15-Aug-2023

The chain of infection is a concept that tells us how infections spread, just like a chain reaction. Understanding the chain of infection is crucial in combating the transmission of diseases. 


As an example, imagine you eat a lovely salad, but a few hours later, find yourself violently sick. What happened to you? Most likely, you may have got food poisoning from raw lettuce in the salad.


When this type of infection happens to a few more people, public health agencies trace how the infection spreads through a community. This is a standard process in infection control. And breaking the chain can prevent more large-scale outbreaks.


There are six essential links in the chain of infection:


  • The infectious agent
  • Reservoirs
  • The portal of exit
  • The mode of transmission
  • The portal of entry
  • The susceptible host


Mapping the chain of infection for a pathogen can help us learn how an infection spreads. This knowledge helps us develop effective strategies to break the chain and reduce the spread of disease.


Understanding the chain of infection

Infectious diseases are caused by organisms like bacteria, viruses, fungi, or parasites. To stop and manage the disease-causing agent, we need to understand how they spread. That is why understanding the chain of infection is important.

Let’s look at the chain of infection in more detail:

Infectious agent

Infectious agents, also known as pathogens, are infection-causing microorganisms, including bacteria, viruses, fungi, and parasites.


The reservoir of an infectious agent is where the agent typically lives, grows, and multiplies. This can be found in humans, animals, or the environment. The reservoir may or may not be the actual source of the agent that infects a host. For instance, the reservoir of Clostridium botulinum is soil. Still, most botulism infections come from improperly canned food with C. botulinum spores.

Portal of exit

The portal of exit is the path a pathogen uses to leave its host. It usually corresponds to where the pathogen is located in the host’s body. For example, influenza and TB exit through the respiratory tract, while cholera and schistosomes exit through feces and urine. Some bloodborne pathogens exit via the placenta (rubella, syphilis, toxoplasmosis). In contrast, others use cuts (hepatitis B) or blood-sucking arthropods (malaria).

Mode of transmission

Transmission happens when an infectious agent moves from its original source or host through an exit point, travels through a specific mode of transfer, and enters a susceptible host through an entry point, leading to an infection.

The primary transmission routes include direct contact, indirect contact, droplet transmission, airborne transmission, vector-borne transmission, and fecal-oral path.

  • Direct contact – The disease can spread when an infected person comes into physical contact with another person. Examples include touching or shaking hands with an infected person. STIs including HIV, syphilis, and gonorrhea are a few examples.
  • Indirect contact – Pathogens can also spread through contaminated surfaces or objects. For instance, touching a door handle previously handled by someone with a common cold could pass on the infection to the uninfected person.
  • Droplet transmission – COVID-19 can spread through droplets produced when an infected person coughs or sneezes.
  • Airborne transmission – Infectious agents can remain suspended in the air over long distances and periods. Tuberculosis is one disease known to be transmitted this way. Measles is one of the examples.
  • Fecal-oral route – The fecal-oral route involves pathogens passing from feces to mouth – usually due to poor sanitation practices. Norovirus would be a classic example.
  • Vector-borne transmission – Vector-borne diseases are transmitted via insects such as mosquitoes. Vector-borne infections like malariadengue, and Lyme disease pose significant health risks worldwide.


Portal of entry

The portal of entry is how a pathogen enters a susceptible host, providing access to tissues where it can multiply, or toxins can act. Many infectious agents use the same entry point to exit the source host and enter a new host. For example, the influenza virus exits and enters the respiratory tract. Others causing gastroenteritis follow a “fecal-oral” route, leaving through feces, contaminating hands, and entering a new host through the mouth via contaminated food, water, or utensils. Additional entry portals include the skin (Hookworm), mucous membranes (Syphilis), and blood (Hepatitis B, HIV).

Susceptible Host

susceptible host is a person or animal who is not immune or resistant to the infectious agent and can contract the disease if exposed. The following factors make a person more susceptible to infections:

  • Age – Older adults and children are more vulnerable to flu and pneumonia.
  • Health conditions – diabetes, heart disease, cancer treatments, and HIV/AIDS.
  • Unhealthy lifestyle choices – smoking, excessive alcohol consumption, and poor diet.
  • The environment – living in crowded or unsanitary conditions.


Breaking the chain of infection: strategies that work

Prevention is the name of the game when it comes to breaking the chain of infection. Effective infection control strategies can be developed only when we clearly understand how infectious diseases spread.


Vaccination is one of the most powerful tools in preventing infectious diseases. It’s like giving your immune system a cheat sheet on how to fight off harmful pathogens. Vaccines train our immune systems to fight specific pathogens, which can break the chain of infection for that infectious agent.

Improved hygiene

Good hygiene practices are crucial in breaking the chain of infection. Regular hand washing with soap and water or using alcohol-based hand sanitizers can help. Individuals can avoid close contact with others who are sick, cover their mouths when coughing or sneezing, and clean high-frequency surfaces more thoroughly. Safe sex practices can mitigate the spread of sexually transmitted infections (STIs).

When working in a healthcare setting, proper protocol must be followed including wearing PPE (personal protective equipment) when required. Patients, medical equipment, and hospital surfaces must be cleaned and disinfected. Contaminated bedding and textiles that come in contact with infected persons must be handled according to infection control standards.

Safe food handling practices

Contaminated foods or liquids can be vehicles for the spread of illnesses. So, make sure you practice safe food handling. Food must be cooked to the proper temperature, cross-contamination should be prevented, and water must be sanitized and clean.

For at-home food safety, the US Centers for Disease Control and Prevention (CDC) recommends 4 steps: clean, separate, cook, and chill to minimize the spread of infection.

Education to spread awareness, not diseases

Raising awareness about infectious diseases and educating people on prevention methods are vital in controlling their spread.

Public health agencies and healthcare professionals must share accurate and clear communication about spreading infections, symptoms, transmission, and treatment options. If vaccines exist, this information can be disseminated, and easily accessible vaccine drives can help break the chain of infection.


Effective treatment can help break chains of infection 

Treatment for infectious diseases may involve medication, lifestyle changes, or a combination of both, depending on the type of infection.

Medications: fighting back against pathogens

Antibiotics, antivirals, or antifungals are common medications available to treat bacterial, viral, or fungal infections. These medications kill or inhibit the growth of the pathogens causing the infection. Learn more about antibiotics from the CDC.

Lifestyle changes: boosting immunity

In addition to medication, lifestyle changes can help communities manage infectious diseases. Following preventive health practices like exercising regularly, improving diets, and regular hand-washing, particularly before eating and after using the restroom can help bolster immunity against infectious diseases.


Understanding the chain of infection is crucial in preventing the spread of infectious diseases. Healthcare professionals and individuals can take proactive measures to break it by taking the necessary precautions.

It’s also important to recognize risk factors that make individuals more vulnerable to infections, such as age, underlying health conditions, lifestyle choices, and environmental factors.

By focusing on prevention strategies like vaccination, good hygiene habits, safe food handling, and spreading awareness, one can significantly reduce the impact of infectious diseases and ensure a healthier future for everyone.

The GIDEON difference

GIDEON is one of the most well-known and comprehensive global databases for infectious diseases. Data is refreshed daily, and the GIDEON API allows medical professionals and researchers access to a continuous stream of data. Whether your research involves quantifying data, learning about specific microbes, or testing out differential diagnosis tools, GIDEON has you covered with a program that has met standards for excellence.

Visit the GIDEON platform to learn more on how to advance the fight against infectious diseases.



[1] “What is the chain of infection and how to break it,” Mun Global, 14-May-2020. [Online]. Available:

[2] CDC,” Centers for Disease Control and Prevention (CDC). [Online]. Available:

[3] L. Spruce, “Transmission-Based Precautions,” AORN J., vol. 112, no. 5, pp. 558–566, 2020.

[4] WHO,  “Vaccines and Immunization,” World Health Organization (WHO). [Online]. Available:

[5] CDC, “Standard precautions for all patient care,” Centers for Disease Control and Prevention (CDC), 25-Mar-2019. [Online]. Available:

[6] CDC, “Foodborne germs and illnesses,” Centers for Disease Control and Prevention, 19-Dec-2022. [Online]. Available:

[7] F. A. Mphande, “Disease awareness and prevention,” in Infectious Diseases and Rural Livelihood in Developing Countries, Singapore: Springer Singapore, 2016, pp. 129–145.

[8] CDC, “Antibiotic use,” Centers for Disease Control and Prevention (CDC), 25-Oct-2022. [Online]. Available:

[9] CDC, “Six tips to enhance immunity,” Centers for Disease Control and Prevention, 21-Jan-2022. [Online]. Available:

[10] CDC, “Recommended Vaccines for Adults,” Centers for Disease Control and Prevention (CDC), 19-May-2023. [Online]. Available:

[11] J. M. van Seventer and N. S. Hochberg, “Principles of infectious diseases: Transmission, diagnosis, prevention, and control,” in International Encyclopedia of Public Health, Elsevier, 2017, pp. 22–39.

[12] CDC, “How Norovirus spreads,” Centers for Disease Control and Prevention, 14-Jun-2023. [Online]. Available:

[13] S. Anand and Y. S. Mayya, “Size distribution of virus laden droplets from expiratory ejecta of infected subjects,” Sci. Rep., vol. 10, no. 1, p. 21174, 2020.

[14] CDC, “Sexually Transmitted Infections,” Centers for Disease Control and Prevention (CDC). [Online]. Available:

[15] CDC, “Rhinoviruses,” Centers for Disease Control and Prevention (CDC), 09-Mar-2023. [Online]. Available:

[16] CDC, “About the division of Vector-Borne Diseases,” Centers for Disease Control and Prevention (CDC), 04-May-2021. [Online]. Available:

Chandana Balasubramanian

Chandana Balasubramanian is an experienced healthcare executive who writes on the intersection of healthcare and technology. She is the President of Global Insight Advisory Network, and has a Masters degree in Biomedical Engineering from the University of Wisconsin-Madison, USA.

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