Legionnaires' disease in Basel: confirmed cases rise to twenty-eight

Confirmed cases of Legionella pneumophila infection in the canton of Basel-Stadt have risen to twenty-eight. The cantonal health department reported two new infections, one of which required admission to hospital.

The outbreak has already caused one death. Six people are currently in hospital. One patient left intensive care the previous day.

The figures refer to the situation at 11am on 5 August and were passed to the Keystone-ATS agency.

Two cooling towers under examination

The suspected origin of the outbreak has been traced to two cooling towers on the roof of Manor's head office, in the Kleinbasel district. Both installations have been shut down and are being analysed.

Evaporative cooling towers work by spraying water to lower the temperature of technical plant. When the water stagnates and reaches favourable temperatures, the bacterium can multiply and disperse into the air along with the droplets.

The Swiss Association for Air and Water Hygiene has commented on how such installations operate. According to the association, "correctly designed evaporative cooling systems maintained to professional standards do not represent a health risk".

That points attention away from the technology and towards its management. Legionnaires' disease is contracted by breathing in contaminated aerosols and does not pass from person to person, which makes identifying the source the decisive step in breaking the chain of infection.

The case count can keep rising even after the installations have been shut down. The interval between exposure and the appearance of symptoms means diagnoses arrive days after infection. At present six of the twenty-eight patients are in hospital.

The department has not said when the results of the analyses on the towers will be available. Nor has it specified how many people may have been exposed in the district concerned. It has not been announced whether other cooling installations in the city have been checked.