Assessing Maintenance of Evaporative Cooling Systems in Legionellosis Outbreaks

Abstract

This study was designed to conduct systematic reviews of existing evaporative cooling system maintenance guidelines and of published Legionnaires’ disease outbreaks to determine what, if any, maintenance practices were in place at the time of the disease outbreaks and then to contrast the reported practices with the published guidelines for evaporative cooling systems. For the first review, similarities in the reported recommendations were assessed; in the second review, any reported information about the state of the evaporative cooling system during the outbreak investigation was summarized. The systematic reviews yielded 38 current guidelines for evaporative cooling systems and 38 published outbreak investigations. The guidelines varied regarding the recommended type and dose of biocides, frequency of general inspections and total system maintenance, the preferred disinfection and cleaning procedures when testing a system for microbiological contamination, the type and frequency of testing procedures, and interpretation of test results. Overall, the maintenance guidelines did not contain sufficiently detailed procedures to prevent the problems that were observed in the outbreak investigations. These maintenance procedures included lack or improper use of a biocide; infrequent testing for microbiological contamination; improper use or maintenance of drift eliminators; and lack of a total system cleaning within 6 months of the outbreak for cooling systems that were either under continuous use, recently started up, or frequently switched on and off. This study suggests that more specific and standardized maintenance guidelines for the control of Legionella bacteria are needed and that these guidelines must be properly implemented to help reduce further Legionnaires’ disease outbreaks associated with evaporative cooling systems.

Keywords:

• cooling towers
• evaporative cooling system
• Legionella pneumophila
• Legionnaires’ disease

ACKNOWLEDGMENTS

A special thanks to the Legionnaires’ Disease Committee members of CTI and ASHRAE for their help in locating some of the evaporative cooling system guidelines.