The Concept of Chain of Infection and Infection Control Principles

For an infectious agent to spread to cause disease, certain conditions must be present. This process is called the chain of infection, which consists of six links: ● Causative agent; ● Infectious reservoir; ● Path of exit; ● Mode of transmission; ● Path of entry; and ● Susceptible host. Infection can occur when all six links are intact. By breaking this chain, the spread of infection can be stopped. ● Causative agent A micro- organism capable of causing infection is called a causative agent. Most commonly they are bacteria, viruses, fungi, and parasites. ● Infectious reservoir A reservoir of infection is the source from which infection can spread by allowing the pathogen to survive and possibly multiply. Humans, animals, and even inanimate environmental objects can serve as reservoirs of infection. There are many sources of infection in a healthcare setting. These include patients, healthcare workers, visitors, inanimate objects like medical equipment, and even the hospital environment. A human reservoir can be either an infected case, or a carrier, i.e. the person is colonized by a particular pathogen and does not present with any symptoms or signs of acute infection. Adherence to standard infection control practices is important as these asymptomatic carriers present a risk of cross infection, especially in healthcare surroundings. ● Path of exit The path of exit is how a pathogen leaves its reservoir. It normally refers to the site where the micro- organism grows. Common sites of exit associated with human reservoirs include the skin, mucous membranes, and the respiratory, gastrointestinal, and genitourinary tracts. ● Mode of transmission The mode of transmission is the route by which an infection spreads. Certain pathogens may use more than one route of transmission from reservoir to host. There are three common modes of transmission. This is the most common mode of infection transmission in a healthcare setting. It can occur either through direct contact when there is direct physical contact with the patient or indirect contact when the pathogen is transmitted from a contaminated intermediate object. Infection spreads through the airborne route when the susceptible person inhales infected particles in droplet nuclei of less than 5 μm.