TABLE 4.
Changes in pathogen occurrence resulting from differences in total chlorine residual in chlorine- or chloramine-treated water at hot- and cold-water tapsa
| Total chlorine residual (mg/liter) | Chlorine |
Chloramine |
Chlorine vs chloramine |
|||||
|---|---|---|---|---|---|---|---|---|
| No. (%) of samples |
P/N ratio | No. (%) of samples |
P/N ratio | Fisher exact testb | P value | |||
| P | N | P | N | |||||
| Cold-water line | ||||||||
| <0.01 | 19 (70) | 8 (20) | 2:1 | 2 (25) | 6 (75) | 1:3 | S | 0.039 |
| 0.1–0.5 | 9 (36) | 16 (64) | 1:2 | 3 (50) | 3 (50) | 1:1 | NS | 0.653 |
| 0.5–1.0 | 9 (36) | 16 (64) | 1:2 | 8 (57) | 6 (43) | 1:1 | NS | 0.314 |
| 1.0–1.5 | 4 (25) | 12 (75) | 1:3 | 8 (80) | 2 (20) | 4:1 | S | 0.005 |
| >1.5 | 5 (42) | 7 (56) | 1:1 | 16 (44) | 20 (56) | 1:1 | NS | 1 |
| Hot-water line | ||||||||
| <0.01 | 36 (56) | 28 (44) | 1:1 | 7 (41) | 10 (59) | 1:1 | NS | 0.289 |
| 0.1–0.5 | 5 (16) | 26 (84) | 1:5 | 5 (62) | 3 (38) | 2:1 | NS | 0.101 |
| 0.5–1.0 | 2 (33) | 4 (67) | 1:2 | 9 (56) | 7 (44) | 1:1 | NS | 0.635 |
| 1.0–1.5 | 0 (0) | 1 (100) | 0:1 | 4 (36) | 7 (64) | 1:2 | NS | 1 |
| >1.5 | 1 (33) | 2 (67) | 1:2 | 13 (59) | 9 (41) | 1:1 | NS | 0.565 |
a
P, a sample with molecular detection of one or more of the microbes measured; N, a sample with no detection of the five pathogens.
b
Cold versus cold and hot versus hot. S, significant; NS, not significant.