Legionnaires’ disease in the EU/EEA*: increasing trend from 2017 to 2019

BACKGROUND: The burden of Legionnaires’ disease (LD) in the European Union/European Economic Area (EU/EEA) has increased during the last decade, with notification rates increasing from 1.2 to 1.4/100,000 population in 2012–16, to 1.8–2.2 within 2017–19. AIM: To measure weekly excess cases during 2017–19 based on previous trends and determine whether a significant change in trend occurred, and to examine any differences in age, sex or level of imported infections. METHODS: We collated 2012–19 annual surveillance data from The European Surveillance System (TESSy) reported by EU/EEA countries. A retrospective prediction by a dynamic regression model was created from 2012–16 data to assess excess cases in 2017–19. Interrupted time series (ITS) analysis was performed to determine if a significant change in trend occurred in 2017–19 compared with the previous 5 years. RESULTS: We found a 33.9% increase in cases in 2017–19 compared with the number predicted. The ITS also found a significant trend increase in 2017–19 compared with 2012–16. A significant trend increase was observed from 2017 most strongly among older age groups (> 60 years) and non-imported cases. CONCLUSION: Our study showed a significant increasing trend in LD cases in the EU/EEA during 2017–19 compared with the previous 5 years. The distribution of cases per week suggests an overall amplification of the seasonal trends. These findings underscore that LD continues to be an infectious disease of public health concern in the EU/EEA, warranting further research into determinants of the increase.