What is the susceptible host in the chain of infection?

The susceptible host is the sixth and final link in the chain of infection. The susceptible host is the person the infectious agent enters and in whom it causes disease. When an infectious agent enters a person, that person does not automatically become sick. A healthy person with no other vulnerabilities can often fight off an infection using the body’s natural defenses. However, when certain risk factors are present, a person is more susceptible to becoming ill. Risk factors include:

• Age, with the very young and the very old being the most vulnerable.
• Genetics.
• Alcoholism or drug addiction.
• Diets that do not provide proper nutrition.
• A compromised immune system, resulting from another disease or from medications that suppress the immune system.
• The need for treatment using an invasive medical device.
• The severity of the illness or injury that brought the patient to the health care facility in the first place.

When an infectious agent causes disease in a susceptible host, the chain of infection is complete. At this point, the new host becomes the reservoir from which the infectious agent might infect others, thereby beginning the chain of infection all over again. This underscores the importance of infection control practices to break this cycle and protect vulnerable individuals and communities.