FATAL NOSOCOMIAL LEGIONNAIRES-DISEASE - RELEVANCE OF CONTAMINATION OFHOSPITAL WATER-SUPPLY BY TEMPERATURE-DEPENDENT BUOYANCY-DRIVEN FLOW FROM SPUR PIPES

The investigation, epidemiology, and effectiveness of control procedur es during an outbreak of Legionnaires' disease involving three immunos uppressed patients are described. The source of infection appeared to be a network of fire hydrant spurs connected directly to the incoming hospital mains crater supply. Removal of these hydrants considerably r educed, but failed to eliminate, contamination of water storage facili ties. As an emergency control procedure the incoming mains water was c hlorinated continuously. Additional modifications to improve tem perat ure regulation and reduce stagnation also failed to eliminate the legi onellae. A perspex test-rig was constructed to model the pre-existing hospital water supply and storage system. This showed that through the hydraulic mechanism known as 'temperature buoyancy', contaminated wat er could be efficiently and quickly exchanged between a stagnant spur pipe and its mains supply. Contamination of hospital storage tanks fro m such sources has not previously been considered a risk factor for Le gionnaires' disease. We recommend that hospital water storage tanks ar e supplied by a dedicated mains pipe without spurs.