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The Chain of Infection


With the pandemic and the new vaccine being distributed, let’s take a look at the chain of infection. The chain of infection includes the conditions that allow for the spread of infection. To break the chain, it is important to eliminate any step in the chain to stop infection, follow practices to interrupt or break the chain, remember that pathogens are everywhere, and remember that prevention is a continuous process. Ways to break the chain of infection include following proper hygiene (hand-washing, cleaning and disinfecting the environment/equipment, wearing proper PPE, etc.), staying up-to-date on vaccinations, covering coughs and sneezes, staying home when sick, and following the rules for standard and contact isolation.

Six Links: The chain of infection consists of six parts, or links: a causative (infectious) agent, reservoir, portal of exit, modes of transmission, portal of entry, and susceptible host.

  1. Infectious Agent​: An infectious agent is a pathogen, such as bacteria, viruses, parasites, and fungi, that can cause disease.

  2. Reservoir:​ A reservoir is an area where the infection can live. A reservoir includes the hiding places for agents, such as fomites, which are objects contaminated with infectious material that contain pathogens (dirty surfaces and equipment like doorknobs, bedpans, urinals, linens, instruments, and specimen containers), the human body, water, animals/insects, the environment, and soil/earth.

  3. Portal of exit:​ The portal of exit is a way for the infectious agent to escape from the reservoir from which it has been growing (respiratory or GI tract, skin, mucous membranes, blood, bodily fluids, aerosols). In the human body, pathogens can leave the body through urine, feces, saliva, blood, tears, mucous discharge, sexual secretions, and draining wounds.

  4. Mode of Transmission:​ The mode of transmission is a way the infectious agent can be transmitted to another reservoir or host where it can live. The pathogen can be transmitted in different ways. One way is by direct contact, which includes person-to-person contact (physical or sexual contact), or contact with a body secretion containing the pathogen. Contaminated hands are one of the most common sources of direct contact transmission. Another way is by indirect contact, when the pathogen is transmitted from contaminated surfaces such as food, air, soil, insects, feces, clothing, instruments, and equipment (airborne/inhalation, droplet, ingestion, etc.). Examples include touching contaminated equipment and spreading the pathogen on the hands, breathing in droplets carrying airborne infections, and contact-vectors (insects, rodents, or small animals), such as being bitten by an insect carrying a pathogen.

  5. Portal of Entry:​ The portal of entry is a way for the infectious agent to enter a new reservoir or host (broken skin/incisions, respiratory tract, breaks in the mucous membranes, digestive tract, genitourinary tract through catheters/tubes, and circulatory system).

  6. Susceptible Host:​ A susceptible host is a person likely to get an infection or disease, usually because body defenses are weak.

BY: Richa Kuklani

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