For the past few days, the canton of Basel-Stadt has been dealing with an unusual outbreak of legionellosis. So far, 26 people have tested positive, 25 have been hospitalised – seven of whom are in intensive care – and one has died. This is not the sort of outbreak caused by negligence at a single facility: the source lies in the cooling towers of an office block in the Kleinbasel district, on Rebgasse. When these towers are contaminated, the aerosols they emit are carried through the air by the wind. People living or working in the surrounding area inhale them without realising it.
Legionella bacteria are well known in the healthcare sector, but many people are unaware that inhaling them in sufficient concentrations can lead to severe pneumonia. There are two forms: Pontiac fever, which is milder and resembles the flu, and Legionnaires’ disease, which can cause a fever of 40 degrees, a severe cough and chest pain. Drinking contaminated water does not pose a risk. The problem lies in inhaling the vapour.
The cantonal authorities have shut down two facilities in the building and are checking the rest. Of the ten facilities tested, eight showed concentrations above the reference values. If you have respiratory symptoms and live near the Kleinbasel neighbourhood, the cantonal medical officer recommends that you see a doctor without delay.
What is striking about this case is that the cooling towers on office buildings are facilities that very few people think of when considering possible sources of infection. Nobody sees them; they are on the rooftops, and if there is no systematic monitoring of bacterial concentrations, the problem can go unnoticed for weeks.