This was done by taking legionella tests in three different types of air humidifiers in district heating plants. The goal of the survey is to get a general picture of the extent of the occurrence of legionella bacteria in different types of air humidifiers. In order to examine if legionella bacteria exists in combustion air humidifiers, and in what quantity, ten different district heating plants where selected for a survey. These conditions consist well with conditions in combustion air humidifiers in district heating plants and therefore it can be suspected that legionella may thrive also in these types of air humidifiers. If a water system furthermore has high levels of other bacteria/microorganisms, then it is also probable that favorable conditions for legionella bacteria exist within the system. The common denominator for most of the sources of infection has been water systems with high oxygen levels and a system temperature ranging from 20 to 40 deg C. The source of infection varies, but in many cases the bacteria has been traced back to cooling towers.
Over the last couple of years several outbreaks of Legionnaires' disease has occurred around the world. Jeppesen, Jessica Hansson, Helen Cederfeldt, Ola Axby, Fredrik Legionella bacteria in combustion air humidifiers Legionella i luftuppfuktare foer foerbraenningsluftĮnergy Technology Data Exchange (ETDEWEB)
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