Legionellosis in Poland in 2018-2021.

Abstract

Objectives: The aim of this study is to compare the epidemiological situation of legionellosis in Poland in 2018-2021 to prior years, taking into account the impact of the COVID-19 pandemic in 2020-2021.

Material and methods: The assessment is based on national surveillance data published in the annual bulletin "Infectious Diseases and Poisons in Poland" from 2013 to 2021, as well as data from Legionnaires' disease case reports collected and sent to the Department of Epidemiology of Infectious Diseases and Surveillance NIPH NIH - NRI by sanitary and epidemiological stations or submitted to EpiBase.

Results: In Poland, both Legionnaires' disease (an acute infection that progresses to pneumonia) and Pontiac fever (a mild, flu-like sickness) are reported. In 2018-2021, a total of 255 cases of legionellosis were registered, including 236 cases of Legionnaires' disease and 19 cases of Pontiac fever. Each year, there was an increase in the number of notifications compared to the annual median number of cases from 2013-2017. The annual incidence rate in 2019 (0.23 per 100,000 population) was the highest since the start of legionellosis case registration in Poland. It declined again during the years of the COVID-19 pandemic. The notifications occurred throughout the country, but the highest notification rate was observed in the western belt of voivodeships. Pomorskie reported the highest incidence, accounting for more than 20% of all registered cases. The median incidence of Legionnaires' disease in men (0.23 per 100,000) was more than twice that of women (0.10), with the highest incidence (0.58) recorded in men 65 years of age or older. All indigenous cases of Legionnaires' disease were sporadic; all but three patients were hospitalized. State Sanitary Inspection reported 26 fatal cases of Legionnaires' disease (mortality = 11%). Twenty-four cases were linked to contaminated water systems in health-care settings, and 21 cases were likely associated with travel abroad.

Summary and conclusions: Although the number of notifications has increased in recent years, Legionnaires' disease is still an infrequently diagnosed respiratory infection in Poland, and the reported incidence remains one of the lowest in the entire EU. The most affected demographic group is men aged 65 and older. Improving the early diagnosis of Legionnaires' disease in healthcare settings remains a priority.