Legionnaires' disease outbreak investigation toolbox

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Decision Support

In a Legionella outbreak, it is important to try to identify the source of exposure in order to control the outbreak and prevent outbreaks in the future, by matching environmental samples with clinical ones. A thorough investigation may provide evidence to link the source of exposure with cases. In some outbreaks, the source of exposure may be obvious from the outset, whilst in others the source may only become apparent after extensive investigations. In addition, there may be the issue of establishing liability, in which case it will be necessary to collect and document evidence in such a way that would stand up to judicial scrutiny.

It is also important to note that, in some outbreaks, the source of exposure may never be established or proven.

This section will thus consider:

Why attempt to match source with cases?

To ensure:

  • Greater assurance that the contaminated source is the cause of the outbreak
  • Implementation of control measures
  • Reduction in size of outbreak
  • Reduction in likelihood of recurrence
  • Limitation of morbidity and mortality resulting from the outbreak
  • Institution of regulatory mechanisms to prevent future cases
  • Recognition of impact of outbreak by case finding
  • Establishment of legal responsibility
  • Development of evidence base and knowledge regarding legionellosis
  • Understanding of outbreak context - i.e. whether international perspective is necessary