Basel Legionella outbreak: One man dead, 25 people in hospital

Basel, A legionella outbreak has claimed one life and hospitalized 25 people in the city over the past two weeks. The infection affected 26 individuals, with seven requiring intensive care. One of the victims was a 69-year-old man with multiple pre-existing conditions who died from the illness. The suspected source of the outbreak was identified as a cooling unit on the roof of an office building located on Rebgasse in Kleinbasel. This unit was shut down on Friday, according to Lukas Engelberger, the city’s health director, who announced the decision during a hastily arranged press conference on Monday afternoon. The decision followed reports of a cluster of cases within a specific neighborhood, prompting authorities to investigate potential environmental factors. Legionella pneumophila, the strain most dangerous to humans among approximately 70 known species, thrives in water temperatures ranging from 25 to 45 degrees Celsius. It can be found in both natural and artificial environments, including water tanks, boilers, showers, bathtubs, and even air conditioning systems. The bacteria remain harmless until they become airborne, typically through fine droplets that enter the lungs and cause severe pneumonia, known as legionnaires' disease. This condition can be fatal in 5 to 10 percent of cases, particularly affecting immunocompromised individuals, smokers, and men over the age of 50. Legionnaires' disease is a notifiable illness in Switzerland, which allowed officials to act swiftly upon identifying the outbreak. The concentration of cases in a single area led investigators to suspect cooling units equipped with wet cooling towers, which emit aerosols capable of spreading through the air. These particles can settle on windowsills, balconies, and sidewalks, where they may be inhaled by passersby. While most infections result in mild symptoms, such as fever, coughing, chest pain, and breathing difficulties, some patients experience headaches, confusion, and gastrointestinal issues. Eva Würfel, deputy cantonal physician, stated that ten such cooling units were examined, with Legionella pneumophila detected in two of them. Other units contained less harmful strains of the bacteria. “Based on current knowledge, we believe the increased risk of legionella contamination for the population has been resolved,” she added. The identification process usually takes more than a week in laboratories, but new methods at the University Hospital of Basel enabled results to be available within hours. Over the past five years, the number of legionnaires’ disease cases in the city has ranged between seven and 20 annually. Nationally, outbreaks occur roughly every few years. Würfel noted a possible increase in recent years, citing studies and the ongoing heatwave as contributing factors. She suggested climate change could play a significant role in this trend. Despite the shutdown of the suspected cooling unit, further investigation is required to confirm its involvement. Genetic comparisons between the bacteria found in patients and those in the cooling unit will take about two weeks. Currently, three of the 26 infected individuals have been confirmed to carry the pathogen. Not all of the affected individuals reside or work in the affected district, leaving room for alternative sources of infection. Authorities caution that additional cases may emerge as the situation continues to unfold.