TABLE 4.
Association of physical, chemical, and microbiologic water characteristics with Legionella contamination
| Characteristic and organism(s) | No. of samples/total (%)
|
RR | P value | |
|---|---|---|---|---|
| Positive for Legionella spp. | Negative for Legionella spp. | |||
| pH of ≥7.8 | ||||
| Legionella spp. | 41/176 (24.1) | 210/828 (25.4) | 0.9 | 0.4 |
| L. pneumophila serogroup 1 | 28/170 (16.5) | 84/128 (10.1) | 1.6 | 0.01 |
| L. pneumophila serogroups 2-14 | 12/170 (7.1) | 102/828 (12.3) | 0.57 | 0.02 |
| Legionella spp. other than L. pneumophila | 1/170 (0.6) | 33/828 (4.0) | 0.14 | 0.012 |
| Sample temp of ≥55 | ||||
| Legionella spp. | 15/145 (10.3) | 239/773 (30.9) | 0.33 | <0.00001 |
| L. pneumophila serogroup 1 | 2/145 (1.4) | 114/773 (14.7) | 0.09 | <0.00001 |
| L. pneumophila serogroups 2-14 | 10/145 (6.9) | 105/773 (13.6) | 0.50 | 0.01 |
| Legionella spp. other than L. pneumophila | 3/145 (2.1) | 29/773 (3.8) | 0.55 | 0.2 |
| Free-chlorine level of ≥0.2 mg/liter | ||||
| Legionella spp. | 14/91 (15.4) | 143/460 (31.1) | 0.49 | 0.001 |
| L. pneumophila serogroup 1 | 3/91 (3.3) | 68/460 (14.8) | 0.22 | 0.0008 |
| L. pneumophila serogroups 2-14 | 8/91 (8.8) | 73/460 (15.9) | 0.55 | 0.05 |
| Legionella spp. other than L. pneumophila | 3/91 (3.3) | 10/460 (2.2) | 1.51 | 0.3 |
| Total plate count of ≥400 CFU | ||||
| Legionella spp. | 83/213 (39.0) | 141/569 (24.8) | 1.57 | 0.00008 |
| L. pneumophila serogroup 1 | 34/213 (16.0) | 78/569 (13.7) | 1.16 | 0.2 |
| L. pneumophila serogroups 2-14 | 39/213 (18.3) | 56/569 (9.8) | 1.86 | 0.0013 |
| Legionella spp. other than L. pneumophila | 13/213 (6.1) | 13/569 (2.3) | 2.67 | 0.01 |