Volume 12, Number 4—April 2006
Research
Reducing Legionella Colonization of Water Systems with Monochloramine
Brendan Flannery*
, 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*
, 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*
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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