Legionnaires' disease outbreak in Basel: Cooling towers identified as likely source

Basel, Switzerland, is grappling with an outbreak of Legionnaires' disease, which has affected 26 people and resulted in one fatality within a two-week period. The rapid spread of the illness has prompted an urgent investigation by cantonal authorities.

Initial findings suggest a common source of contamination within the Petit-Bâle district. Investigations have focused on water cooling towers, as the wind can disperse water vapor containing the bacteria, leading to inhalation by people in the vicinity. Dr. Eva Würfel, deputy cantonal physician, explained that most infections likely occurred outdoors as people walked near contaminated sources.

Testing of ten cooling systems revealed that eight had Legionella bacteria levels exceeding authorized limits. The specific species responsible for most human infections, Legionella pneumophila, was detected in two systems, which have since been permanently shut down. These installations were located on the roof of an office building in the Kleinbasel area.

Legionella bacteria are naturally present in water but become dangerous when they multiply in artificial water systems and are inhaled. Contamination occurs through inhaling tiny water droplets, not by drinking the water. Symptoms of Legionnaires' disease, the severe form, include fever, cough, muscle pain, and headaches, potentially leading to severe pneumonia. The mortality rate for Legionnaires' disease is between 5% and 10%, even with antibiotic treatment. A milder form, known as Pontiac fever, also exists.

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Most people would have been contaminated in the street. The wind disperses the water vapor from the cooling towers, which reaches people when the water particles fall back down.