Legionella in Cooling Towers

Legionellosis (Legionnaires' disease and Pontiac fever) outbreaks have been associated with aerosols ejected from contaminated cooling towers — wet-type heat rejection units (WTHRUs) used to dissipate unwanted heat into the atmosphere. The Vermont Department of Health undertook a program to inv...

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Bibliographic Details
Published in:Journal of environmental health 1986-11, Vol.49 (3), p.134-139
Main Authors: Witherell, Linden E., Novick, Lloyd F., Stone, Kenneth M., Duncan, Robert W., Orciari, Lillian A., Kappel, Steven J., Jillson, David A.
Format: Article
Language:English
Subjects:
Air Conditioning - standards
Cooling towers
Data Collection
Disease outbreaks
Environmental Exposure
Epidemiology
Groundwater
Humans
Legionella
Legionella pneumophila
Legionellosis
Legionnaires disease
Legionnaires' Disease - epidemiology
Maintenance and Engineering, Hospital - standards
Surface water
Turbidity
Vermont
Water Microbiology
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Summary:Legionellosis (Legionnaires' disease and Pontiac fever) outbreaks have been associated with aerosols ejected from contaminated cooling towers — wet-type heat rejection units (WTHRUs) used to dissipate unwanted heat into the atmosphere. The Vermont Department of Health undertook a program to inventory, inspect, and sample all WTHRUs in Vermont from April 1981 to April 1982. All WTHRUs were sampled for Legionella pneumophila and data were obtained for location, design, construction, and operating characteristics. Of the 184 WTHRUs operating, statistical analyses were performed on those 130 which were sampled for L. pneumophila only once during the study period. Of these, 11 (8.5%) were positive for L pneumophila. Source of makeup water and period of operation had significant association with the recovery of L. pneumophila. Five out of 92 towers (5.4%) utilizing surface water sources for cooling were positive for L. pneumophila, in contrast to 6 positive towers of the 38 units (15.8%) which obtained makeup water from ground water sources (p= .054 by chi-square test). Nearly 15% of the 54 units which operated throughout the year were positive, compared to less than 4% of the 76 towers operating seasonally (p= .03 by chi-square test). The mean pH of the cooling water in units where L. pneumophila was recovered (8.3) was significantly higher than the mean pH of 7.9 in units testing negative (p < .05 by t-test). In addition, the mean log-transformed turbidity of positive towers, 0.03 nephelometric units (ntu), was significantly lower than the mean of log turbidity of negative towers, 0.69 ntu (p < .02 by t-test).
ISSN:0022-0892