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. 2018 Dec 2:148:w14687.
doi: 10.4414/smw.2018.14687. eCollection 2018 Nov 19.

A community outbreak of Legionnaires' disease in Geneva, Switzerland, June to September 2017

Marie-Céline Zanella  1 , Sabine Yerly  1 , Abdessalam Cherkaoui  2 , Gesuele Renzi  2 , Aline Mamin  1 , Laura Lourenço Cordes  3 , Elisabeth Delaporte  4 , Zofia Baranczuk-Turska  5 , Olivia Keiser  6 , Jacques Schrenzel  2 , Stephan Harbarth  7 , Valeria Gaia  8 , Laurent Kaiser  1
Affiliations
Free article

A community outbreak of Legionnaires' disease in Geneva, Switzerland, June to September 2017

Marie-Céline Zanella et al. Swiss Med Wkly. .
Free article

Abstract

Purpose: Eight confirmed cases of Legionnaires’ disease were identified at the Geneva University Hospitals between 28 July 2017 and 02 August 2017, leading to a detailed outbreak investigation.

Methods: Legionnaires’ disease cases were defined according to Swiss and European (ELDSNet) consensus guidelines. An outbreak investigation task force was put in place. Patients were interviewed, when feasible, with a standard questionnaire. A Legionella pneumophila urinary antigen test was performed in all cases. Lower respiratory tract (LRT) specimens were collected for culture, polymerase chain-reaction (PCR) assay, monoclonal antibody subtyping and sequenced-based typing (SBT). Multiple environmental samples were collected. Case geographical mapping was performed and local meteorological data were obtained.

Results: Thirty-four confirmed cases of Legionnaires’ disease were identified between 20 June 2017 and 16 September 2017, including 28 patients living in the Canton of Geneva and 6 cases in neighbouring cantons and France. The case fatality rate was 8.8%. The urinary antigen test was positive in 32/34 (94.1%) cases. Among the 17/34 (50%) cases with available LRT specimens, 8 (47.1%) were culture/PCR positive, 5 (29.4%) were PCR positive only, and 4 (23.5%) were culture/PCR negative. Monoclonal antibody subtyping and SBT on 12 samples allowed subtype identification of 8 samples, with a predominance of L. pneumophila serogroup-1 subtype-France/Allentown ST23 among clinical isolates. A specific city area was identified as a possible outbreak epicentre in 25/34 (73.5%) cases, although molecular analysis of clinical and environmental specimens revealed heterogeneous subtypes of L. pneumophila.

Conclusions: In this largest documented outbreak of Legionnaires’ disease in Switzerland, we report prompt outbreak identification, leading to timely initiation of a detailed, well-orchestrated clinical and epidemiological investigation.

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