Analytical methods for Legionnaires' disease outbreak investigation

A number of GIS-based investigative techniques can be considered (depending on the data available) when responding to a Legionnaires' disease outbreak. The techniques described below all have their 'pros and cons' and should not be viewed as for use in isolation. The techniques should be viewed as complementary and used as such.

1.1 Data visualisation

Data requirements: Case data, Potential outbreak source locations.

Data can be visualised in a number of ways to gain insight into the spatio-temporal characteristics of an outbreak.

1.2 Outbreak Detection

Data requirements: Case data

A variety of space-time cluster surveillance techniques have been used to identify Legionnaires' disease outbreaks.

1.3 Comparing potential outbreak sources

Data requirements: Case data, Potential outbreak source locations, Demographic data

By exploring the spatial relationships that exist between each case and potential source locations it is possible to identify the most likely source(s) responsible for an outbreak.

1.4 Inferring an outbreak source location

Data requirements: Case data

By analysing the areas in space occupied by each case, in the time period before their onset of symptoms, it is possible to identify areas in common between cases that may be suggestive of a common infection source location.

1.5 Airborne dispersion modelling

Data requirements: Case data, Potential outbreak source locations, Meteorological data

Plume modelling can attempt to describe the downwind dispersal of contaminated aerosols from potential outbreak source locations. The outputs of plume models can be brought into GIS and be used to assess whether the pattern of infection is consistent with a modelled release.

1.6 GIS Software

There are a number of GIS packages capable of perform the analyses described in sections 1.1 - 1.5, both open source and close source.