System Theory

EHS-Net work is based on system theory. System theory is “a general science of wholeness“: rather than dissecting a complex process and studying the individual parts, system theory focuses on understanding the complete system and the underlying interactions of all the forces that make up that system.

In the 1940s, Ludwig von Bertalanffy introduced the concept of system theory, which he described as a general science of wholeness. He went on to say,

"classical science tried to isolate the elements of the observed universe, expecting that, by putting them together again, the whole or system would result and be intelligible. Now we have learned that for an understanding, not only the elements, but their interrelations as well, are required"

Therefore, a system is a set of elements that interact to achieve a goal. Systems are usually made up of four major elements:

• Input (the energy or material that goes into the system)
• Processes (the actions that happen within the system that transforms the input)
• Output (what results from the processes)
• Feedback (the information that is produced that can be used to evaluate and monitor the system)

In system theory, it is important to remember the whole is more than the sum or its parts. Dynamic interactions among the parts can often result in characteristics of the whole that are not the same as the characteristics of the separate parts. Change in one part of the system may affect the other parts or the whole.

Food Service as a System

A food-service establishment is an example of a system. The outcome of the system (food served to customers) is influenced by the factors that make up the system, such as ingredients, food workers, equipment, preparation/cooking processes, and the economics of the establishment.
EHS-Net uses system theory to identify environmental antecedents (underlying factors) to illness and disease outbreaks.

Read about how the systems approach has been used to investigate foodborne outbreaks:

• Dippold L, Lee R, Selman C, Monroe S, Henry C. A gastroenteritis outbreak due to norovirus associated with a Colorado hotel. J Environ Health. 2003;66(3):13-7
• Higgins CL, Hartfield, BS. A systems-based food safety evaluation: an experimental approach. J Environ Health. 2004;67(4) 9–14.

Water System Theory

To understand how water becomes contaminated and therefore possibly causes illness, we must understand and examine the entire system of drinking water delivery. We must know the facilitators and barriers in the water system that may lead to illness. In addition, we must understand the relation among host, agent, and environment.

Read about how the systems approach has been used in a waterborne disease outbreak investigation:

• Gelting R, Sarisky J, Selman C, Otto C, Higgins C, Bohan PO, Buchanan SB, Meehan PJ. Use of a systems-based approach to an environmental health assessment for a waterborne disease outbreak investigation at a snowmobile lodge in Wyoming. Int J Hyg Environ Health. 2005;208(1–2):67–73.

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