Guidelines for the Prevention and Control of Influenza Outbreaks in Residential Care Facilities for Public Health Units in Australia
3.1 Introduction
There is a clear distinction between a definition used to define an outbreak of respiratory disease and one used to define cases within an outbreak. The key objective of formulating an ‘outbreak definition’ is to assist staff at a RCF to easily decide if an outbreak of respiratory disease may be occurring and thence to alert the PHU in a timely fashion. Key criteria to be considered are how many purported cases exist and in what timeframe. The outbreak definition should be relatively simple and more emphasis should be placed on ensuring the definition is a sensitive rather than a specific one. An early role of the PHU is to decide whether the report represents a true outbreak, is not an outbreak at all, or if additional information needs to be collected to increase certainty.
The main use for the ‘case definition’ is for use by the outbreak management team once an outbreak has been declared. The main reasons for having a case definition are:
(i) to be able to identify cases early in order to institute disease control efforts to benefit that person and to limit the risk of transmission to others, and
(ii) to accurately describe the outbreak to facilitate effective overall outbreak management and for epidemiological/research purposes.
The case definition should be established early in the outbreak and modified if necessary to ensure it is both reasonably sensitive and specific. The definition given here is for guidance only and will vary according to the pathogen and the demographics and underlying health status of the residents within the facility. Key criteria will include symptomatology (‘person’), timing of symptom onset (‘time’), and possibly location within the facility (‘place’). The case definition developed for residents may be different from that developed for staff.
