Bg. Shelton et al., LEGIONNAIRES-DISEASE OUTBREAKS AND COOLING-TOWERS WITH AMPLIFIED LEGIONELLA CONCENTRATIONS, Current microbiology, 28(6), 1994, pp. 359-363
This study was designed to investigate the possible association of hig
h colony counts of legionellae from cooling towers and evaporative con
densers with Legionnaires' disease outbreaks. We obtained legionellae
counts from samples of cooling towers and evaporative condensers that
were the likely sources of two different Legionnaires' disease outbrea
ks and compared these counts with those from cooling towers that were
not associated with reports of human disease. Among 675 potential cont
rol cooling tower water samples from 258 facilities, 136 facilities ha
d one or more cooling towers that met our criteria for inclusion into
the study. Samples taken from buildings where an outbreak had occurred
had much higher Legionella counts than did samples from other buildin
gs. Colony counts from the two outbreak-associated facilities were sig
nificantly higher than colony counts from other facilities [Wilcoxon R
ank Sum Test (Exact), p < 0.01]. The results of the study suggest that
, among cooling towers that test positive for the presence of legionel
lae, higher colony counts are associated with higher risk of Legionnai
res' disease.