The World Health Organization announced on Thursday that Poland has recorded 23 deaths linked to Legionnaires' disease as of September 11. The organization reported a total of 166 cases of the disease, with no new cases reported since September 7. The illness is caused by the bacteria (Legionella), which can lead to a severe form of pneumonia. The WHO states that the most common way for the infection to spread is through inhaling contaminated airborne droplets originating from water sprays, cooling towers, or mist from contaminated water sources. Authorities stated in August that the Polish Internal Security Agency is investigating whether the disease outbreak was due to deliberate tampering with the water system. The organization added that the source of infection has not yet been identified and that investigations are still ongoing to determine the source of the outbreak.