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Table 1 Growth of Legionella spp. and total bacterial count (p-value compares results of water samples from old filters to results from new filters)

From: Impact of a silver layer on the membrane of tap water filters on the microbiological quality of filtered water

   number of Legionella positive samples number of samples >100 CFU per mL in total bacterial count at 22°C number of samples >100 CFU per mL in total bacterial count at 36°C
unfiltered water (n = 60)   29 (48.3%) 18 (30.0%) 33 (55.0%)
   old filter (n = 20) new filter (n = 40) p-value old filter (n = 20) new filter (n = 40) p-value old filter (n = 20) new filter (n = 40) p-value
filtered water at different usage intervals 7 days 0 (0.0%) 1 (2.5%) 1.000 3 (15.0%) 0 (0.0%) 0.033 2 (10.0%) 0 (0.0%) 0.107
  14 days 0 (0.0%) 0 (0.0%) 1.000 9 (45.0%) 10 (25.0%) 0.146 4 (20.0%) 8 (20.0%) 1.000
  21 days 0 (0.0%) 0 (0.0%) 1.000 10 (50.0%) 18 (46.2%)** 0.787 9 (45.0%) 20 (50.0%) 0.788
  28 days 0 (0.0%) 0 (0.0%)* 1.000 9 (45.0%) 25 (64.1%)* 0.177 14 (70.0%) 27 (69.2%)* 1.000
  1. * Only 39 samples were tested due to leakage of the adaptor between one filter and its water tap.
  2. ** Only 39 samples were tested due to laboratory contamination during processing of one sample.