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:
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.