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Chain of Infection: Definition & Example

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  • 0:00 Definition: The Chain…
  • 0:39 The Six Links
  • 2:42 Example of a Chain of…
  • 3:06 Control Measures
  • 3:36 Lesson Summary
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Lesson Transcript
Instructor: John Koshuta
Infectious disease results from the interaction of an agent, a host, and an environment. Most of these diseases follow a typical chain of infection that ends with an infected host. Understanding the chain of infection can help with both the prevention and treatment of infectious diseases.

Definition: The Chain of Infection

How do viruses pass from one person to the next? When one child has a cold at school, why is the rest of the class likely to come down with one the next week? Let's explore how infection gets from one place to another, or the chain of infection.

chain of infection

The chain of infection, if we think of it as an actual chain, is made up of six different links: pathogen (infectious agent), reservoir, portal of exit, means of transmission, portal of entry, and the new host. Each link has a unique role in the chain, and each can be interrupted, or broken, through various means.

The first link is the pathogen itself. This is the disease-causing organism. For many illnesses and diseases this is a virus or bacterium. In order to break this link, various methods can be used, including the pasteurization of milk, the chlorination of drinking water, or the use of disinfectants.

The second link is the reservoir. This is the natural environment that the pathogen requires for survival. Reservoirs can be a person, an animal, or an environmental component, such as soil or water. This link can be broken through medical treatment and testing, insect and rodent eradication, or quarantine.

The third link is the portal of exit. This link is needed for the pathogen to leave the reservoir. If the reservoir is a human, then the portal of exit may be saliva, mucous membranes, feces, blood, or nose or throat discharges. By using barrier methods, such as condoms or masks, or covering the mouth while coughing, this link can be broken.

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