SwissLEGIO - Legionnaires' diseases in Switzerland: Prestudies to develop health systems and epidemiologic research

Legionella spp. are common environmental bacteria living in freshwater. They are also known to proliferate in artificial water reservoirs such as cooling towers or showerheads. Infection with the bacteria may lead to legionellosis, a group of diseases ranging from a mild, flu-like illness (Pontiac fever) to potentially fatal pneumonia, known as Legionnaires’ disease (LD). The true burden of disease due to Legionella spp. is unknown. The estimates are primarily based on data from disease surveillance systems, in which currently legionellosis is included in mostly high-income countries with well-functioning health systems. In Switzerland, cases of legionellosis are reported to the Federal Office of Public Health (FOPH) since December 1987. Ever since, the number of notifications steadily increased, and more than doubled in the last 15 years.

To better understand the legionellosis epidemiology in Switzerland, we conducted a series of studies focusing on the pathway from exposure of the patient to Legionella spp. to disease notification. A first study, a so-called positivity study, investigated the proportion of positive cases to the number of diagnostic tests performed for Legionella spp. between 2007 and 2016. The results show a strong increase in testing frequency among diagnostic laboratories while case numbers increased proportionally. The cause of the increase in testing is unclear and testing behaviour might be different across Swiss regions.

Understanding the health systems context. The literature study comprised a scoping review of current national and international guidelines, recommendations and legal regulations (i) on the prevention and control of Legionella spp. infection and contamination, (ii) on the diagnostic pathway and the case management of pneumonia patients (including potential LD patients) and (iii) on disease surveillance and (iv) outbreak investigations. Among other findings, the results of the scoping review showed that LD case investigations in Switzerland are conducted mainly by local authorities on a cantonal level. A comprehensive and nationally standardised LD outbreak investigation toolbox is currently lacking. As a result, applied procedures to address LD outbreaks within Switzerland are heterogeneous and the responsibilities of different stakeholders are not well defined. This may hamper a successful and timely detection of the outbreak’s infection source. In the European Union and the US, such outbreak toolboxes are available and can be openly consulted.

Exploring physicians’ management of pneumonia:  This study was conducted to better comprehend diagnostic pathways among care providers to identify a case of LD. We found that diagnostic testing for Legionella spp. is limited to the hospital setting. There, the majority of patients are tested using rapid diagnostic tests. In the ambulatory care setting, patients are primarily treated empirically without identification of the causative agent and more severe cases of pneumonia are referred to the hospital. This is in line with current guideline recommendations for the management of community-acquired pneumonia.

Patients’ perspective of Legionnaires’ disease: Finally, a study among patients aims at investigating the patients’ experience and perceived burden and causes of LD. The study acts as a pilot study for a subsequent Case-Control and molecular source attribution study on Legionnaires’ disease to explore the risk factors and exposure sites for contracting Legionnaires’ disease in Switzerland.

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

Fischer F.B, Deml M.J, Mäusezahl D. Legionnaires' disease: a qualitative study on Swiss physicians' approaches to the diagnosis and treatment of community-acquired pneumonia. Swiss Med Wkly. 2022;152:w30157. DOI: 10.4414/smw.2022.w30157

Fischer F.B, Mäusezahl D, Wymann M.N. Temporal trends in legionellosis national notification data and the effect of COVID-19, Switzerland, 2000-2020. Int J Hyg Environ Health. 2023;247:113970. DOI: 10.1016/j.ijheh.2022.113970

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