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Eurosurveillance, Volume 10, Issue 23, 09 June 2005

Citation style for this article: Nygård K, Outbreak investigation collaborators. Update: Outbreak of legionnaires’ disease in Norway traced to air scrubber. Euro Surveill. 2005;10(23):pii=2719. Available online:

Update: Outbreak of legionnaires’ disease in Norway traced to air scrubber

Karin Nygård1 (, on behalf of the outbreak investigation collaborators*

1Nasjonalt folkehelseinstitutt (Norwegian Institute of Public Health), Oslo, Norway

As of 8 June 2005, 55 cases of legionnaires’ disease including ten deaths have been diagnosed associated with an outbreak in southeast Norway [1,2]. The mean age of patients is 69 years, the median 66 years. All of the patients are Norwegian residents; 33 are men and 22 are women. The last case was in a patient who fell ill on 25 May.

The outbreak investigation included:

  1. a population-based retrospective cohort study where the exposure was the location of the cases’ residence in relation to several potential sources, and the outcome was legionnaires’ disease;
  2. a comparison of patient and environmental samples by restriction fragment length polymorphisms (RFLP) and random amplification of polymorphic DNA (RAPD) methods.

Both approaches indicated the same source, an air scrubber in a lignin production plant. The scrubber cleans particles in the air used in the production process by exposing it to a strong counterflow of water. The water in the scrubber has a high organic content and is circulated by a pump. A continuous input of fresh water helps to keep the dry-matter level constant and replace water lost as aerosol. The scrubber operates at 40°C and expels more than 4 cubic metres of water/hour as aerosol, with an airflow of 60 000 cubic metres/hour and velocity of about 20 metres/second. The tank of the scrubber was routinely cleaned with high-pressure hot water every 3-4 weeks, but no disinfection was used. The pump and pipes had not been manually cleaned.

The scrubber has been closed and there are no risks to tourists visiting the area or to other parts of Norway.

A risk assessment of air scrubbers regarding conditions facilitating legionella growth (such as temperature and biofilm formation) must be done when investigating outbreaks of legionellosis.

*The outbreak investigation collaborators include: Fredrikstad and Sarpsborg municipalities, Nasjonalt folkehelseinstitutt, Sykehuset Østfold Fredrikstad, Telelab, Norsk Matanalyse, Universitetssykehuset Nord-Norge, Norsk institutt for luftforskning, and Geodata AS.

  1. Legionellasmitten kom trolig fra et skrubberanlegg. Sarpsborg kommune, press release 9 June 2005. (,43043&_dad=portal&_schema=PORTAL&articleId=7658&artSectionId=720)
  2. Blystad H, Brantsæter AB, Løvoll Ø. Outbreak of community-acquired legionnaires’ disease in southeast Norway, May 2005. Eurosurveillance weekly release 2005; 10(5): 26/5/2005. (

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