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Filter efficacy (mean cfu/ml at 22°C) of filter type 1–3
| Operating time (weeks) | trial 2/filter type 1 (n samples) | trial 3 (filter type 2) (n samples) | trial 4 (filter type 3) (n samples) |
| 1 | 3.1 ± 5.9 (78) | 7.3 ± 8.8 (54) | 14.4 ± 17.5 (18) |
| 4 | - | 20.0 ± 27.4 (54) | 3.8 ± 4.6 (18) |
| 8 | - | - | 6.3 ± 11.5 (18) |
