Elderly individuals are generally more susceptible to contracting illnesses. This increased vulnerability is often attributed to their typically weaker immune systems.

Elderly Susceptibility to Illness

Examples of factors that may make a host more susceptible to infection or disease are genetics, resiliency, nutritional status, prior exposure, age, co-infection, etc.


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Traditional model for infectious disease that consits of an agent/pathogen, a susceptible host, and an environment.  Disease is a result of an agent/pathogen and a susceptible host interacting in an environment that enables transmission. 

Epidemiological Triangle

Reference of Foundations of Large Language Models Course

In infectious disease epidemiology, an agent is an infectious organism or pathogen, such as a virus, bacterium, paraiste, etc. that can cause disease. 
Some factors that can influence an agent's ability to cause disease include: pathogenicity, virulence, addictive qualities, infectivity, ability to survive outside body, susceptibility to antibiotics, etc. 


Agent/Pathogen

Qualities that can affect an environment or its susceptibility include: climate, building design, sanitation, social environment, access to health care, population density, etc.


Environment

The traditional sequence in which infectious disease results from the interaction of agent, host, and environment.


Chain of Infection

Host susceptibility

A vector is an organism which transmits infection by conveying the pathogen from one host to another without causing disease itself, may be part of the infectious process.

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