Chain of infection

The chain of infection. The chain of infection describes how residents patients, client,s health care workers or any members of the general public can acquire an infection. Each link in the cycle show how the organism that cause disease can be transferred. If we want to prevent the spread of infection, including antibiotic resistant infections, we need to break a link in this chain. Okay, so let’s start at the top. An infectious agent - the organism can be a drug resistant bacterium, such as MRSA or clostridium difficile. These infectious agents grow and multiply in a reservoir, and reservoirs can be humans, animals and even the environment. Rather annoyingly human reservoirs may or may not show the effects of an illness.

In fact, a carrier can be a person who seems to be well. They have no symptoms of the infectious disease but they are still capable of transmitting the pathogen to others. These asymptomatic, passive, or healthy carriers never experience symptoms of illness, despite being infected. Other carriers include incubatory carriers, who transmit the infectious agents during the incubation period, before clinical illness begins. Convalescent carriers have recovered from the illness but remain capable of transmitting the infectious agent to others - and chronic carriers continue to harbour potentially infectious germs for months, or even years after the initial infection.

Okay, because carriers do not know they are infected, they are more likely to spread the infection than someone who is aware that they are ill, and this is because they - the people who are ill are likely to take special precautions to prevent transmission. If you have an animal that can also act as a reservoir then the term zoonosis can be used and this refers to infectious diseases such as, salmonella, that are transmitted from animals to humans. Other bacteria such as, the bacteria that cause Legionnaires disease, exist in the environment and in places and reservoirs, such as, water and the soil. Next the exit route, or the portal of exit.

And this is the path that the pathogen uses to leave its host and it’s usually the site where the bacterial pathogen is found in the body. For example, Mycobacterium tuberculosis is the bacterium that causes TB, which infects the lungs. It exits the body in respiratory tract secretions such as small droplets, ejected in coughs and sneezes. Then, we have the method of spread, or the mode of transmission, so an infectious agent can be transmitted from its natural reservoir to a susceptible host in different ways.

In direct transmission, an infectious agent is transferred from a reservoir to a susceptible host by direct contact that includes skin-to-skin contact, for example, when you’re kissing, or through sexual intercourse, but direct contact can also refer to contact with soil, or vegetation that harbours infectious organisms. Gonorrhea is an example of a disease that is spread from person to person through direct contact. On the other hand, indirect transmission is an infectious agent that moves from a reservoir via an inanimate objects such as, handkerchiefs, bedding or surgical scalpels.

Now there are also vectors that can carry infectious diseases, and fleas are an example because they can carry the bacterium Yersinia pestis, which is responsible and still responsible for spreading the plague from rats to humans. Next, we have the entry route, or the portal of entry and this is how a pathogen can enter a susceptible host. It must provide access to human tissues used by the pathogen it must provide access to the human tissues used by the pathogen to multiply.

Often, infectious agents use the same portal of entry to enter a new host that they used to exit the same host, for example TB exists in the respiratory tract of the source host and it enters the respiratory tract of a new host, but some pathogens exit the host in faeces and are carried on unwashed hands directly to the mouth, or on unwashed hands via vehicles such as food or water, or a kitchen utensil before entering a new host through the mouth. Other the portals of entry include the skin and moist mucous membranes, as well as blood. Finally, we have the host, or the person who’s at risk as well. And this is the final chain.

And in the chain of infection some individuals are naturally more immune to some infectious agents than others. They have natural protection against infection. Humans are covered with skin that protects the inside tissues from infections and they have acid in their stomach and cilia in the respiratory tract that sweep microbes up from the lung to protect the lungs from becoming infected. And humans also have antibodies that protect them from getting specific infectious diseases. So there we have it. We have the chain of infection. It is quite complicated and you can see that, at any stage, if we can just break the links that are there, we’re going to minimise the chance of passing infection from one person to another.