International Journal of Epidemiology, Vol 28, 353-359, Copyright © 1999 by International Epidemiological Association
CM Brown, PJ Nuorti, RF Breiman, AL Hathcock, BS Fields, HB Lipman, GC Llewellyn, J Hofmann and M Cetron
BACKGROUND: From July to September 1994, 29 cases of community-acquired
Legionnaires' disease (LD) were reported in Delaware. The authors conducted
an investigation to a) identify the source of the outbreak and risk factors
for developing Legionella pneumophila serogroup 1 (Lp- 1) pneumonia and b)
evaluate the risk associated with the components of cumulative exposure to
the source (i.e. distance from the source, frequency of exposure, and
duration of exposure). METHODS: A case- control study matched 21 patients
to three controls per case by known risk factors for acquiring LD. Controls
were selected from patients who attended the same clinic as the respective
case-patients. Water samples taken at the hospital, from eight nearby
cooling towers, and from four of the patient's homes were cultured for
Legionella. Isolates were subtyped using monoclonal antibody (Mab) analysis
and arbitrarily primed polymerase chain reaction (AP-PCR). RESULTS: Eleven
(52%) of 21 case-patients worked at or visited the hospital compared with
17 (27%) of 63 controls (OR 5.0, 95% CI : 1.1-29). For those who lived,
worked, or visited within 4 square miles of the hospital, the risk of
illness decreased by 20% for each 0.10 mile from the hospital; it increased
by 80% for each visit to the hospital; and it increased by 8% for each hour
spent within 0.125 miles of the hospital. Lp-1 was isolated from three
patients and both hospital cooling towers. Based on laboratory results no
other samples contained Lp-1. The clinical and main-tower isolates all
demonstrated Mab pattern 1,2,5,6. AP-PCR matched the main- tower samples
with those from two case-patients. CONCLUSION: The results of our
investigation suggested that the hospital cooling towers were the source of
a community outbreak of LD. Increasing proximity to and frequency of
exposure to the towers increased the risk of LD. New guidelines for cooling
tower maintenance are needed. Knowing the location of cooling towers could
facilitate maintenance inspections and outbreak investigations.
ARTICLES
A community outbreak of Legionnaires' disease linked to hospital cooling towers: an epidemiological method to calculate dose of exposure
Centers for Disease Control and Prevention Epidemiology Program Office, Division of Field Epidemiology, Atlanta, GA 30333, USA.
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