Swiss Tropical and Public Health Institute, Allschwil, Switzerland; University of Basel, Basel, Switzerland.
Barcelona Institute for Global Health (ISGlobal), Barcelona, Spain.
Environ Res. 2023 Sep 15;233:116327. doi: 10.1016/j.envres.2023.116327. Epub 2023 Jun 22.
The number of reported cases of Legionnaires' disease (LD) has risen markedly in Switzerland (6.5/100,000 inhabitants in 2021) and abroad over the last decade. Legionella, the causative agent of LD, are ubiquitous in the environment. Therefore, environmental changes can affect the incidence of LD, for example by increasing bacterial concentrations in the environment or by facilitating transmission.
The aim of this study is to understand the environmental determinants, in particular weather conditions, for the regional and seasonal distribution of LD in Switzerland.
We conducted a series of analyses based on the Swiss LD notification data from 2017 to 2021. First, we used a descriptive and hotspot analysis to map LD cases and identify regional clusters. Second, we applied an ecological model to identify environmental determinants on case frequency at the district level. Third, we applied a case-crossover design using distributed lag non-linear models to identify short-term associations between seven weather variables and LD occurrence. Lastly, we performed a sensitivity analysis for the case-crossover design including NO levels available for the year 2019.
Canton Ticino in southern Switzerland was identified as a hotspot in the cluster analysis, with a standardised notification rate of 14.3 cases/100,000 inhabitants (CI: 12.6, 16.0). The strongest association with LD frequency in the ecological model was found for large-scale factors such as weather and air pollution. The case-crossover study confirmed the strong association of elevated daily mean temperature (OR 2.83; CI: 1.70, 4.70) and mean daily vapour pressure (OR: 1.52, CI: 1.15, 2.01) 6-14 days before LD occurrence.
Our analyses showed an influence of weather with a specific temporal pattern before the onset of LD, which may provide insights into the effect mechanism. The relationship between air pollution and LD and the interplay with weather should be further investigated.
在过去十年中，瑞士（2021 年每 10 万居民中有 6.5 例）和国外报告的军团病（LD）病例数量显著增加。军团菌是 LD 的病原体，在环境中无处不在。因此，环境变化会影响 LD 的发病率，例如增加环境中的细菌浓度或促进传播。
本研究旨在了解环境决定因素，特别是天气条件，对瑞士 LD 地区和季节性分布的影响。
我们基于 2017 年至 2021 年瑞士 LD 通知数据进行了一系列分析。首先，我们使用描述性和热点分析来绘制 LD 病例并识别区域集群。其次，我们应用生态模型在区县级别上识别与病例频率相关的环境决定因素。第三，我们应用病例交叉设计，使用分布式滞后非线性模型，确定七种天气变量与 LD 发生之间的短期关联。最后，我们对病例交叉设计进行了敏感性分析，其中包括 2019 年可用的 NO 水平。
瑞士南部的提契诺州在聚类分析中被确定为热点地区，标准化报告率为 14.3 例/10 万居民（CI：12.6，16.0）。在生态模型中与 LD 频率相关性最强的是天气和空气污染等大尺度因素。病例交叉研究证实，每日平均温度升高（OR 2.83；CI：1.70，4.70）和每日平均水汽压升高（OR：1.52，CI：1.15，2.01）与 LD 发生前 6-14 天有很强的关联。
我们的分析表明，天气对 LD 发病前有影响，且具有特定的时间模式，这可能为发病机制提供了新的认识。空气污染与 LD 之间的关系以及与天气的相互作用应进一步研究。
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