An outbreak of legionnaires disease caused by long-distance spread from an industrial air scrubber in Sarpsborg, Norway.
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 degrees 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.
Nygård
Karin
K
Norwegian Institute of Public Health, Oslo, Norway. karin.nygard@fhi.no
Werner-Johansen
Øyvind
Ø
Rønsen
Svein
S
Caugant
Dominique A
DA
Simonsen
Øystein
Ø
Kanestrøm
Anita
A
Ask
Eirik
E
Ringstad
Jetmund
J
Ødegård
Rune
R
Jensen
Tore
T
Krogh
Truls
T
Høiby
E Arne
EA
Ragnhildstveit
Eivind
E
Aaberge
Ingeborg S
IS
Aavitsland
Preben
P
D000328:Adult; D000336:Aerosols / Q000737:chemistry; D000368:Aged; D000369:Aged, 80 and over; D000389:Air Conditioning; D000391:Air Microbiology; D015331:Cohort Studies; D004196:Disease Outbreaks; D004866:Equipment Contamination; D005260:Female; D006801:Humans; D016952:Legionella pneumophila / Q000302:isolation & purification*; D007877:Legionnaires' Disease / Q000453:epidemiology* / Q000382:microbiology; D008297:Male; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D012189:Retrospective Studies; D014871:Water Microbiology
D000336:Aerosols