How to Stop the Spread: Breaking the Chain of Infection

Infection Control Definition of the Chain of Infection

Infection does not occur without the presence of the essential elements leading to it. These elements are an infectious agent, a source for this agent, and a susceptible host. Most importantly, there must be a method by which the infectious agent is transmitted to the host. The interaction between all these elements is known as the ""Chain of Infection"" or the ""Disease Transmission Cycle,"" focusing on the links and relationships between all these elements"".

Infection Control Definition of the Components of the Disease Transmission Cycle or Chain of Infection

1- Infectious Agents: These are microbes that can cause infection or disease, including ""bacteria, germs, viruses, fungi, or parasites"".

2- Infectious Reservoir: This is the place where disease-causing microbes live, grow, and multiply. It could be humans, animals, plants, soil, air, water, or other solutions, tools, or equipment used in hospitals that may harbor disease-causing microbes"".

3- Exit Portals: This refers to the path through which the infection or infectious agents exit. Through it, the infectious organism can leave the reservoir via the bloodstream or openings in the skin, such as ""superficial or deep wounds, surgical sites, or skin rashes"". Also, mucous membranes such as the ""nose, mouth, eyes, respiratory system like lungs, as well as the urinary tract, reproductive system, and digestive system like the mouth or anus"" or the placenta, through blood, secretions, or droplets coming from these parts of the body"".

4- Modes of Transmission: Infection control refers to the path through which the microbe travels from the reservoir to the host or the person susceptible to infection. There are five ways these infectious agents are transmitted:

Contact

The infectious organism may be transmitted directly from the reservoir to the susceptible host through touch, such as ""Staphylococci bacteria"". Also, sexual relations, for example, ""Gonorrhea or Human Immunodeficiency Virus (HIV/AIDS)"". Contact is considered the most important and common mode of infection transmission in hospitals and can be divided into two types: 1- Direct Contact: Refers to the transmission of microbes resulting from the touch of an infected person's body surface with another susceptible person's body surface. 2- Indirect Contact: Refers to the susceptible person's contact with a contaminated material such as contaminated medical equipment, needles, bandages, the contaminated hands of healthcare providers, or contaminated gloves that are not changed when dealing with patients.

Droplet Transmission

Refers to the transmission of disease-causing microbes through droplets containing microbes produced by the infected source while speaking, sneezing, or coughing, or resulting from certain medical procedures like bronchoscopy or respiratory suctioning devices. These contaminated droplets spread through the air for a short distance not exceeding one or two meters and enter the body of the susceptible host through the mucous membranes of the nose, mouth, or eyes. Droplets are characterized by a density that does not allow them to remain suspended in the air, meaning that microbes transmitted via droplets are different from those transmitted via air; therefore, there is no need for special ventilation techniques to prevent transmission through this path"".

Airborne Transmission

Infectious agents may be transmitted via very small droplet nuclei, less than five microns, containing microorganisms that remain suspended in the air, which carries them over long distances unlike large or small droplets. The susceptible host then inhales these small nuclei, such as ""Measles and Tuberculosis"". These small nuclei remain suspended in the air for varying periods, and here, good ventilation methods are beneficial in preventing microbe transmission"".

Vehicle Transmission

Infectious microbes may be transmitted indirectly to the host or susceptible person through a substance contaminated with the infectious agent. These vehicles include food, such as ""Salmonella""; blood, such as ""Hepatitis B and C viruses"" and HIV; and water, such as ""Cholera and Shigella"".

Vector-Borne Transmission

Here, the disease-causing microbe can be transmitted to the susceptible host through insects and other invertebrates, such as ""Mosquitoes,"" which transmit ""Malaria, Yellow Fever, and Rift Valley Fever,"" and fleas that transmit the ""Plague"".

5- Portals of Entry: These represent the paths the disease-causing microbe takes to enter the susceptible host's body. Infection control defines them as follows "".

• *- Bloodstream {through devices like intravenous catheters or injections}
• *- Skin openings {superficial and deep wounds, skin rashes, and surgical sites}
• *- Mucous membranes {nose, eyes, and mouth}
• *- Urinary and reproductive systems
• *- Digestive system {anus and mouth}
• *- Placenta

6- Susceptible Host: This is the person who can be infected by disease-causing microbes. This host could be the patient, a healthcare worker in a health facility, hospital staff, visitors, etc. The host varies depending on the infectious agent or disease. Vaccination against certain types of infectious microbes helps reduce infections caused by these microbes"".

Example: How Hepatitis B virus can be transmitted within hospitals or medical facilities:

1- Infectious Reservoir: The person carrying the Hepatitis B virus, often a chronic patient.

2- Exit Portals from the Reservoir: The exit portals from the Hepatitis B patient's body are through the bloodstream in its various forms.

3- Modes of Transmission: Hepatitis B transmission occurs through needles previously used by the patient or tools.

4- Portals of Entry: The entry portals for Hepatitis B are through wounds of various types.

5- Susceptible Host: This person could be a medical or healthcare provider in hospitals or medical facilities. Infection occurs if everything used is not properly sterilized"".

See also: How is infection control managed within health facilities?