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 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. Sources 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 less than .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 less than .02 by t-test).

Duration of whirlpool-spa use as a risk factor for Pseudomonas dermatitis.

Pseudomonas dermatitis occurred among 16 of 49 whirlpool-spa bathers in a Vermont hotel during a weekend in November 1983. Pseudomonas aeruginosa, serotype 0:4, was isolated from a patient and the whirlpool-spa water. Since duration of whirlpool-spa use had been previously postulated as a risk factor for dermatitis, a historical cohort study was designed to test this hypothesis. Each bather was carefully interviewed about the duration in minutes of whirlpool-spa and swimming pool exposure on the weekend. Total duration of whirlpool-spa use was significantly associated with rash illness both on contingency and logistic regression analysis. Females were also found to be at increased risk, after controlling for the study hypothesis. Duration of whirlpool-spa use was an important determinant of risk for Pseudomonas dermatitis in this outbreak.