Conditions favourable to the growth of microorganisms are sometimes found in mechanical ventilation and air-conditioning systems. Where such microorganisms are potentially pathogenic or allergenic, human respiratory ailments such as Legionnaires' disease and humidifier fever can result. The paper reviews the incidence of these illnesses and describes the circumstances in which the causal organisms can develop. Basic information on building services systems is given and possible means of airborne transmission of microorganisms are considered. Preventive measures include attention to simple regular maintenance procedures such as the cleaning of water reservoirs and inspection of filters. Biocidal water treatment is a possible additional control measure to minimize growth of microorganisms in cooling towers.
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