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. 2013 Sep 10;32(20):3522-38.
doi: 10.1002/sim.5765. Epub 2013 Mar 11.

A case-association cluster detection and visualisation tool with an application to Legionnaires' disease

P Sansom  1 , V R Copley, F C Naik, S Leach, I M Hall
Affiliations

A case-association cluster detection and visualisation tool with an application to Legionnaires' disease

P Sansom et al. Stat Med. .

Abstract

Statistical methods used in spatio-temporal surveillance of disease are able to identify abnormal clusters of cases but typically do not provide a measure of the degree of association between one case and another. Such a measure would facilitate the assignment of cases to common groups and be useful in outbreak investigations of diseases that potentially share the same source. This paper presents a model-based approach, which on the basis of available location data, provides a measure of the strength of association between cases in space and time and which is used to designate and visualise the most likely groupings of cases. The method was developed as a prospective surveillance tool to signal potential outbreaks, but it may also be used to explore groupings of cases in outbreak investigations. We demonstrate the method by using a historical case series of Legionnaires' disease amongst residents of England and Wales.

Keywords: Legionnaires’ disease; case-association; cluster; detection; visualisation.

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Figures

Figure 1
Figure 1
Sporadic community-acquired cases of Legionnaires’ disease in England and Wales from 1980 to 2007. Bars represent the observed number of cases per week, and the curve represents the number of cases per week predicted by the background temporal model.
Figure 2
Figure 2
Attack ratio per 10 000 population of sporadic community-acquired cases of Legionnaires’ disease, 1980–2007, by census ward. Attack ratio defined as (total number of sporadic community cases 1980–2007/total ward population at 2001 census). A total of 8850 census wards are represented in the map. Contains Ordnance Survey data © Crown copyright and database rights 2013. Contains National Statistics data © Crown copyright and database right 2013.
Figure 3
Figure 3
Single groupings of more than 11 cases identified by model at 0.15 distance level from complete data series; excludes Barrow-in-Furness outbreak.
Figure 4
Figure 4
Frequency of outbreak sizes given by case series and modelled groupings at 0.15 distance level.
Figure 5
Figure 5
Dendrograms for the major outbreaks identified in Table 3, showing case groupings at 0.15 distance level using the data associated with empirically derived outbreak cases only.
See this image and copyright information in PMC

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