Clinical Infectious Diseases 2008;46:61–69
An Outbreak of Legionnaires Disease Caused by Long-Distance Spread from an Industrial Air Scrubber in Sarpsborg, Norway
挪威一起因空气除尘设施被污染而导致的军团病暴发
Karin Nygård,1 Øyvind Werner-Johansen,3 Svein Rønsen,4 Dominique A. Caugant,1 Øystein Simonsen,5. Anita Kanestrøm,5 Eirik Ask,6 Jetmund Ringstad,5 Rune Ødegård,7 Tore Jensen,2 Truls Krogh,1 E. Arne Høiby,1 Eivind Ragnhildstveit,5 Ingeborg S. Aaberge,1 and Preben Aavitsland1
1Norwegian Institute of Public Health and 2Geodata, Oslo, 3Municipal Health Services, Sarpsborg, 4Municipal Health Services and 5Østfold Hospital Trust, Fredrikstad, 6Telelab, Skien, and 7Norwegian Institute for Air Research, Kjeller, Norway
Received 22 June 2007; accepted 24 August 2007; electronically published 30 November 2007.
Presented in part: 6th International Conference on Legionella, Chicago, Illinois, October 2005 (abstract 154).
Reprints or correspondence: Dr. Karin Nygård, Div. of Infectious Disease Control, Norwegian Institute of Public Health, Pb 4404 Nydalen, NO-0403 Oslo, Norway (karin.nygard@fhi.no).
Background. On 21 May 2005, the Norwegian health authorities were alerted by officials from a local hospital that several recent patients had received the diagnosis of legionnaires disease; all patients resided in 2 neighboring municipalities. We investigated the outbreak to identify the source and to implement control measures.
Methods. We interviewed all surviving case patients and investigated and harvested samples from 23 businesses with cooling towers and other potential infection sources. The locations of the businesses and the patients' residences and movements were mapped. We calculated attack rates and risk ratios among people living within various radii of each potential source. Isolates of Legionella pneumophila were compared using molecular methods.
Results. Among 56 case patients, 10 died. The case patients became ill 12–25 May, resided up to 20 km apart, and had not visited places in common. Those living up to 1 km from a particular air scrubber had the highest risk ratio, and only for this source did the risk ratio decrease as the radius widened. Genetically identical L. pneumophila serogroup 1 isolates were recovered from patients and the air scrubber. The air scrubber is an industrial pollution-control device that cleans air for dust particles by spraying with water. The circulating water had a high organic content, pH of 8–9, and temperature of 40°C. The air was expelled at 20 m/s and contained a high amount of aerosolized water.
Conclusions. The high velocity, large drift, and high humidity in the air scrubber may have contributed to the wide spread of Legionella species, probably for >10 km. The risk of Legionella spread from air scrubbers should be assessed. |
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