Geneva Health Forum 2024

SwissLEGIO - Legionnaires’ disease in Switzerland: A national case-control and molecular source attribution study

Not scheduled

15m

Geneva

Oral presentation Health and the environment, time for solutions

Description

Introduction: Switzerland has one of the highest annual Legionnaires’ disease (LD) notification rates in Europe (7.6 cases/ 100,000 population in 2022). The main sources of infection and the cause for this high rate remain largely unknown. This hampers the implementation of targeted Legionella spp. control efforts. The SwissLEGIO national case-control and molecular source attribution study investigates risk factors and infection sources for community-acquired LD in Switzerland. The study is conducted in an inter- and transdisciplinary approach involving various national governmental and national research stakeholders.
Methods: Between July 2022 and March 2024, the study recruits 205 newly diagnosed LD patients through a network of 20 secondary- and tertiary hospitals across Switzerland. Healthy controls matched for age, sex, and residence at the district level are recruited from the general population. Risk factors for LD are assessed in questionnaire-based interviews. Clinical and environmental Legionella spp. isolates are compared using whole genome sequencing (WGS). Direct comparison of sero- and sequence types (ST), core genome multilocus sequencing types (cgMLST), and single nucleotide polymorphisms (SNPs) between clinical and environmental isolates are used to investigate infection sources and the prevalence and virulence of different Legionella spp. strains detected across Switzerland.
Results: As of December 2023, we have enrolled 183 patients, and collected 486 household water samples from 76 case- and 52 control households. In collaboration with various cantonal authorities, we collected an additional 93 samples from other potential infection sources in the environment. A first batch of 39 clinical and 133 environmental isolates are fully sequenced and analysed. The sequencing of this first batch revealed matches of clinical and environmental isolates from the Southern part of Switzerland. Sequencing of clinical and environmental Legionella isolates is ongoing.
Conclusion: WGS is used increasingly in LD outbreak investigations and other epidemiological studies including those attributing environmental infection sources to human Legionellosis cases. Analysing sequencing data of Legionella spp. in the context of a rich set of epidemiological metadata is particularly powerful and essential for effective infection source attribution. However, several questions still need to be addressed regarding the recovery strategies of Legionella spp. from clinical and environmental samples, biobanking, secure data storage, and comparability of WGS results. We present results from our large-scale national SwissLEGIO case-control study. We discuss results from the sequencing of clinical and environmental Legionella spp. isolates and some first lessons learnt on the applicability of WGS in this context.