GeoLEGIO: Legionnaires’ disease in Switzerland: A spatial analysis of notification data from 2017-2021

Legionnaires’ disease (LD) is a severe form of pneumonia caused by Legionella spp. bacteria. The disease is notifiable to the Swiss Federal Office of Public Health (FOPH). Over the past ten years, annual reported incidence rates of LD in Switzerland are continuously increasing. The reason for this increase and the main sources of infection for LD remain unknown. In this research project, we are investigating Swiss notification data on LD from 2017 to 2021. The project focuses on spatial analysis and correlations of notified cases with exposures.

Legionella spp. is ubiquitously present in the environment, with stagnant and warm (25-42°C) water and soil being its preferred reservoirs. Transmission to humans occurs via inhalation of bacteria-contaminated aerosols. Therefore, most water reservoirs, natural or artificial, can act as infectious sources and the identification of the source for a particular LD case is challenging. As a result, the main drivers for LD infections, their regional distribution and their impact on the risk for the population remain unknown.

Previous analysis of LD notification data in Switzerland showed that cases are not distributed homogeneously across the cantons. Yet, the spatial information from the notification system on LD has not been analysed systematically beyond cantonal levels. We used geographic information systems (GIS) to map notified LD cases between 2017 and 2020, potential infection sources and other risk determinants for LD to enhance our understanding of the current geographical distribution and spatial correlates within Switzerland.

The results from our cluster analysis showed high notification rates of LD in the canton of Ticino and a region with lower than expected rates in the Eastern part of Switzerland. In an aggregated analysis of exposure sources and notification rates on a district level, we also observed that air pollution, relative humidity and population parameters, such as mean age and the social deprivation index were associated with LD notification rates.

To investigate the impact of meteorological events and air pollution on reported LD incidences in more depth, we are currently conducting an analysis that captures the short-term and transient effects of these exposures.

The developed methodology and the collected exposure data within the GeoLEGIO project will be applied to the case and control data obtained within the SwissLEGIO study.

Fischer F.B, Fanderl J, Mäusezahl D. Zeitliche Entwicklung und Einfluss verschiedener Faktoren auf die räumliche Verteilung der Legionärskrankheit in der Schweiz. BAG Bulletin. 2022;3:8-11

Fischer F.B, Schmutz C, Gaia V, Mäusezahl D. Legionnaires’ disease on the rise in Switzerland: a denominator-based analysis of national diagnostic data, 2007–2016. Int J Environ Res Public Health. 2020;17:7343. DOI: 10.3390/ijerph17197343

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