Principles of Epidemiology in Public Health Practice, Third Edition
An Introduction to Applied Epidemiology and Biostatistics
[www.cdc.gov/csels/dsepd/ss1978/lesson1/section8.html](https://www.cdc.gov/csels/dsepd/ss1978/lesson1/section8.html) 

Concepts of Epidemiology in Public Health Practice

- Crowding (increases the risk of spreading the virus)
- Atmosphere (if the disease is airborne)
- Phenomena that bring the host and agent together (in relation to the environment)
        - vector (e.g. mosquitoes, bats)
        - vehicle (more contact surfaces for the virus to spread)
        - reservoir (e.g. animals to humans)

Environmental Factors

Urbanization refers to an increased movement and settling of people in urban surroundings. Rapid urbanization leads to the development of heterogeneous living environments, such as slums, shanty towns, and wealthy neighborhoods. The differences between these environments can pose several health risks, which leads to an increase of infectious diseases in urban environments.

Urbanization and Epidemiology

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


University of Michigan - Ann Arbor

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

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

Environment

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


Chain of Infection

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.


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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