Aetiological agent
The agent (eg bacteria, virus) that causes the illness.

Available chlorine

Free chlorine expressed as a percentage of active ingredient in a concentrated liquid or powder.

Care facility

Includes aged care facilities, special accommodation facilities, hospitals, child day care centres.

Case control study

A study which starts with the identification of persons with the disease of interest and a suitable control group of persons without the disease. The relationship of an attribute to the disease is examined by comparing the diseased and non-diseased with regard to how frequently the attribute is present or, if quantitative the levels of the attribute, in each of the groups. Case control studies are sometimes called "retrospective studies." In relation to gastrointestinal illness they are usually undertaken to test a hypothesis that a certain type of food caused the illness to occur by comparing the ill (cases) with well people (controls). Controls are usually matched with the cases for sex, age and postcodes.

Case finding

A process or method used to find additional cases of an illness being investigated. Examples used may be to contact doctors, laboratories, hospitals, cases etc.

Cohort study

The method of epidemiological study in which subsets of a defined population can be identified who are, have been or in the future may be exposed or not exposed or exposed in different degrees, to a factor or factors hypothesised to influence the probability of occurrence of a given disease or other outcome. Whilst cohort studies are sometimes referred to as "prospective studies" in relation to gastrointestinal outbreaks cohort studies are undertaken after the event has occurred. However a cohort study is only appropriate when the number of exposed persons can be identified (eg an outbreak at a wedding etc).

Communicable disease

A disease which is capable of being transmitted from one person or species to another

Contact

A person or animal who has been in association with an infected person or animal or a contaminated environment and who may have thereby acquired infection.

Cross-contamination

The spread of micro-organisms from one surface to another or from something that is contaminated to something that is not.

Disinfection

The specific killing of infectious agents outside the body by direct exposure to chemicals or physical agents.

Epidemic curve

A histogram or bar chart showing the time-course of the outbreak on the horizontal axis, with the number of cases on the vertical axis. Time may be expressed as either specific dates, or as time since exposure if that is known. (eg hours or days, depending on what is appropriate.)

Fomes (Plural fomites)

Object such as a book, wooden object or an article of clothing that is not harmful in itself but is able to harbour pathogenic mico-organisms and thus may serve as an agent of transmission of an infection.

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HACCP (Hazard Analysis and Critical Control Point)

A system which identifies, evaluates and controls hazards which are significant for food safety.

Index case

The first case in a family or other defined group to come to the attention of the investigator.

Infection control

The process of minimising the risks of spreading infection.

Incubation period

The time between initial contact with an infectious agent and the appearance of the first sign or symptom of the disease.

Institution

Refers to any establishment for care or education eg. hospital, nursing home, college etc.

Isolation

The process of separating infected or colonised persons from others, usually for as long as the organism may practically be communicated to other susceptible persons. Isolation usually occurs in places and under conditions to prevent or limit the direct or indirect transmission of the infectious agent to susceptible persons.

Primary case

The individual who introduces the disease into the family or group under study. Not necessarily the first diagnosed case in a family or group. See also Index Case

Sanitise

To reduce pathogenic micro-organisms to a safe level.

Secondary case

Case of disease occurring among contacts within the incubation period following exposure to the primary case.

Special care facility

Includes aged care facilities, special accommodation facilities, special developmental schools etc.

Standard precautions

See Guidelines for the Control of Infectious Diseases (The Blue Book) Appendix 4, p. 223.

Sterilisation

The complete destruction or elimination of all living micro-organisms, including bacterial spores.

Guidelines for the investigation of gastrointestinal illness index