Abstract
The risk of falling ill with Legionnaires’ disease (LD) is suggested to increase, but the global burden of disease is unknown due to a lack of appropriate diagnosis and surveillance systems. In Switzerland, the number of LD cases, captured by the National Notification System for Infectious Diseases, has more than doubled since 2008. This study aims to investigate this increase, contextualizing disease surveillance data with denominator data, which is not routinely available, i.e., the number of tests performed for Legionella spp. We collected the testing data for Legionella spp. of 14 Swiss diagnostic laboratories and calculated the positivity, defined as the proportion of the number of positive tests to the number of tests performed. The number of positive tests increased proportionally to the number of tests performed; hence, the positivity remained stable. However, the cause of the increase in test volume is unclear and has a large impact on the interpretation of the positivity curve. Further, the test outcome was found to be dependent on regional determinants, and the diagnostic method applied. The lack of understanding if and at which stage LD is considered in current case management of pneumonia patients limits the interpretation of observed heterogeneities in incidence or underestimation of LD in Switzerland. The absence of (or non-adherence to) existing guidelines and the heterogeneity in diagnostic testing hampers the comparison of data in the Swiss public health context. Therefore, diagnostic procedures should be harmonised across Switzerland and adherence to national LD management guidelines supported.
Highlights
Legionella spp. are the cause of a group of diseases termed “legionellosis” ranging from mild and self-limiting Pontiac fever to potentially fatal Legionnaires’ disease (LD), characterized by pneumonia [1,2]
14 Swiss diagnostic laboratories andperformed calculatedtothe positivity,the i.e., the We proportion thetesting number ofof positive tests to the number of tests investigate the proportion in the number of positive to the number of tests performed to investigate the increase observed in case numbers of LD intests official disease surveillance
We found that men were more often tested for Legionella spp. than women were, and positivity was significantly higher for males than for females
Summary
Legionella spp. are the cause of a group of diseases termed “legionellosis” ranging from mild and self-limiting Pontiac fever to potentially fatal Legionnaires’ disease (LD), characterized by pneumonia [1,2]. Infections with Legionella spp. occur through inhalation or aspiration of contaminated water or aerosols. Legionella spp. occur worldwide, the global burden of disease is unknown due to the lack of appropriate diagnosis and/or surveillance systems in many countries. In Europe in 2017, 1.8 cases per 100,000 population were estimated, corresponding to 9238 cases in total. The US reported 7500 cases, corresponding to 2.3 cases per 100,000 population [4,5]. Case numbers have been increasing in European countries and the US in the past years
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