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Volume 12, Number 4—April 2006

Research

Reducing Legionella Colonization of Water Systems with Monochloramine

Brendan Flannery*Comments to Author , Lisa B. Gelling†, Duc J. Vugia‡, June M. Weintraub§, James J. Salerno¶, Michael J. Conroy¶, Valerie A. Stevens*, Charles E. Rose*, Matthew R. Moore*, Barry S. Fields*, and Richard E. Besser*
Author affiliations: *Centers for Disease Control and Prevention, Atlanta, Georgia, USA; †California Emerging Infections Program, Oakland, California, USA; ‡California Department of Health Services, Richmond, California, USA; §City and County of San Francisco Department of Public Health, San Francisco, California, USA; ¶San Francisco Public Utilities Commission, Burlingame, California, USA

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Table 4

Factors associated with Legionella colonization at point-of-use outlets in sampled buildings, San Francisco, California

Factor No. samples % Legionella colonization Adjusted prevalence ratio (95% CI)* p value
Residual disinfectant
Chlorine 617 39 Referent
Chloramine 627 1 0.04 (0.02–0.09) <0.001
Water heater colonized with Legionella spp.
Yes 182 74 1.74 (1.26–2.40) <0.001
No 1,062 11 Referent
Temperature of water at point-of-use outlet, °C
<30 23 13 Referent
30–39 268 24 0.90 (0.39–2.08) 0.8
40–49 786 22 0.85 (0.35–2.05) 0.7
>50 175 10 0.75 (0.29–1.90) 0.5
Building height (stories)
3–10 855 15 Referent
>10 397 31 1.85 (1.46–2.35) <0.001
Disruption in service in last 3 mo
Yes 142 23 1.34 (0.99–1.81) 0.06
No 1,109 20 Referent

*Prevalence ratios and 95% confidence intervals (CIs) were adjusted for repeated sampling and correlations between samples taken from the same building and for the effects of all other variables. Twenty-eight observations were missing.

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