On Sept. 14, 2023, the World Health Organization (WHO) reported that as of Sept. 11, 2023, a total of 166 cases of legionellosis, including 23 deaths, had been reported from Poland. Legionellosis, more commonly known as Legionnaires’ disease, is a pneumonia-like illness, caused by a bacterium, that varies in severity from mild to a severe illness and sometimes fatal form of pneumonia.

This observed increase in confirmed cases, and associated hospitalizations and deaths seen since mid-August, is unusual, considering that the number of cases is higher than the annual number reported in Poland since 2016.