Industrial air scrubbers may spread disease

NEW YORK (Reuters Health) - An industrial pollution-control air scrubber in Sarpsborg, Norway has been identified as the source of an outbreak of Legionnaires disease that occurred in May 2005, according to health officials who investigated the outbreak.

Legionnaires disease is a severe form of pneumonia caused by bacteria in water droplets.

Fifty-six people diagnosed with Legionnaires became ill between May 12 and May 25; and 10 of them died. All 56 people lived up to 20 kilometers (about 12 miles) apart and had not visited places in common.

"Case patients" living close to a particular industrial air scrubber (up to 1 kilometer away) had the highest "risk ratio" for Legionnaires disease and only for this source did the risk of illness decrease as the radius widened, investigators report in the journal Clinical Infectious Diseases.

Moreover, genetically identical strains of Legionella -- the bacterium that causes Legionnaires -- were recovered from infected patients and the air scrubber.

The high velocity, large drift, and high humidity in the air scrubber -- an industrial pollution-control device that cleans air for dust particles by spraying with water -- may have contributed to the wide spread dissemination of Legionella, the investigators suggest.

"We think that this outbreak emphasizes the importance of considering all potential aerosol-producing devices in an outbreak of Legionnaires disease -- not only the well-known (i.e. cooling towers)," Dr. Karin Nygård, a senior epidemiologist in the division for infectious disease control at the Norwegian Institute of Public Health, Oslo, told Reuters Health.

"If the environmental conditions in the scrubber are favorable for Legionella growth, industrial air scrubbers may, under certain conditions, be very potent disseminators of aerosols, as shown by the widespread transmission in this outbreak," she added.

"The risk of Legionella spread from air scrubbers should be assessed," the investigators conclude.

SOURCE: Clinical Infectious Diseases, January 1, 2008.