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Table 1 Levels of free residual chlorine, trihalomethanes and Legionella isolation according to chlorination stage

From: Legionella control in the water system of antiquated hospital buildings by shock and continuous hyperchlorination: 5 years experience

Chlorination stage Residual free chlorine mg/L Trihalomethanes μg/L Legionella spp. Samples without point of use filters Legionella spp. Samples with point of use filters
  Arithmetic mean SD Median IQ Range Arithmetic mean SD Median IQ Range Positive Total Positive Total
Before hyperchlorination 0.19 0.56 0.10 0.05 - 0.20 2.71 1.81 2.38 1.36 - 3.17 43 (21.1%) 204 0 4
15 days after hyperchlorination 0.34 0.73 0.18 0.10 - 0.25 8.70 6.61 7.50 3.95 - 12.5 15 (7.8%) 193 0 18
30 days after hyperchlorination 0.23 0.18 0.20 0.11 - 0.30 8.55 3.52 7.84 6.38 - 11.30 6 (3.5%) 173 0 20
Continuous hyperchlorination 0.61 0.34 0.60 0.40 - 0.79 10.7 23.8 5.50 2.76 - 10.01 23 (5.5%) 416 0 222
No continuous hyperchlorination 0.15 0.15 0.12 0.07 - 0.17 1.05 1.07 0.88 0.66 - 2.62 15 (27.8%) 55 0 3
Total 0.43 0.44 0.30 0.13 - 0.65 8.97 18.56 5.40 2.58 - 9.87 102 (9.8%) 1041 0 267