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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 2

Prevalence of Legionella colonization and concentrations in hot water systems in buildings in San Francisco, California, by residual disinfectant and sampling interval*

Water source Chlorine (2003)
Chloramine (2004)
Jan–May Jun–Jul Oct–Dec Mar–May Jun–Aug Sep–Dec p value†
Building water systems (n = 53)
No. colonized with Legionella spp. (%) 27 (51) 34 (64) 35 (66) 5 (9) 0 2 (4) <0.001
Median no. Legionella-positive samples in colonized buildings (range)‡ 3 (1–9) 3 (1–8) 4 (1–8) 1 (1–4) 1 (1–2) 0.007
Water heaters (n = 53)
No. colonized with Legionella spp. (%) 12 (23) 16 (30) 17 (33) 1 (2) 0 0 <0.001
Median Legionella concentration in colonized water heaters, CFU/mL (range)‡ 200 (40–400) 40 (10–500) 20 (10–5,000) 10 0.17
Point-of-use outlets (n = 212)
No. colonized with Legionella spp. (%) 75 (37) 85 (41) 86 (41) 7 (3) 0 2 (1) <0.001
Median Legionella concentration in colonized sites, CFU/mL (range)‡ 2.5 (0.05–25.0) 1.5 (0.05–25.0) 1.0 (0.05–25.0) 0.05 (0.05–0.40) 0.18 (0.10–0.25) <0.001

*Percentages calculated based on number of samples included in analyses (see Methods).
†For Wilcoxon rank sum test comparing number of sites colonized with Legionella spp. before and after the conversion to chloramine disinfectant.
‡Includes only Legionella-positive sites.

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