These guidelines have been produced to assist in the investigation of both sporadic cases and outbreaks of gastrointestinal illness. They are designed in a manner which guides investigations from the time of notification, through the initial investigation to the control and clean-up phases. The guidelines also outline further strategies to prevent future cases and identify educational opportunities.

Investigation of cases and outbreaks of gastrointestinal illness enables identification of problems and initiation of action to prevent further illness.

Infectious disease surveillance enables:

• The identification of trends in the community which may signify an outbreak
• The initiation of action to prevent or minimise outbreaks
• The measurement of prevalence of disease in the population
• Evaluation of control and prevention measures
• Opportunities to educate the public in disease prevention
• The planning of services and priority setting

The control of communicable disease outbreaks is best achieved when changes in disease incidence are detected early.

Gastrointestinal illness may occur as apparently sporadic cases, as small clusters of cases, or as point source outbreaks which may be small or large and may last from hours to months.

Most cases of gastrointestinal illness in the community are sporadic and often the precise route of transmission is not discovered.

Common viral, bacterial and protozoan enteric pathogens are transmitted by the faecaloral route, however, the path from excretion by an infected person or animal to ingestion by the next case may be obscure and complicated. Transmission of the pathogen may occur by close person to person contact, contaminated environmental surfaces, fomites, food or water.

In most instances it will be difficult or impossible to definitely determine the source of a person's illness. Nevertheless, the public health significance of cases of gastrointestinal illness which come to the attention of health authorities must be appraised, and even if an individual case is not formally investigated, it should still be reported because monitoring disease trends over time is an important function of surveillance. It is also an important opportunity to educate the public in disease prevention.

Guidelines for the investigation of gastrointestinal illness index