Microbes in filter backwash samples (n = 161) from metro-Atlanta pools, by select characteristics
| Characteristic . | PCR positive for E. coli (N = 93)an (%) . | p-valueb . | PCR positive for P. aeruginosa (N = 95)an (%) . | p-valueb . |
|---|---|---|---|---|
| Location | ||||
| Outdoor (n = 104) | 60 (58) | 1.000 | 67 (64) | 0.067 |
| Indoor (n = 57) | 33 (58) | Ref. | 28 (49) | Ref. |
| Setting | ||||
| Municipal (n = 37) | 26 (70) | 0.048 | 22 (59) | 0.843 |
| Waterpark (n = 35) | 23 (66) | 0.114 | 18 (51) | 0.316 |
| Membership/Club (n = 89) | 44 (49) | Ref. | 55 (62) | Ref. |
| Primary patron designation | ||||
| Primarily children (n = 15) | 11 (73) | 0.274 | 10 (67) | 0.595 |
| Adults and children (n = 145) | 81 (56) | Ref. | 85 (59) | Ref. |
| Stabilized chlorine usage | ||||
| No (n = 90) | 53 (59) | 0.751 | 51 (57) | 0.522 |
| Yes (n = 71) | 40 (56) | Ref. | 44 (62) | Ref. |
| Time since last backwash | ||||
| 1–3 days (n = 85) | 44 (52) | 0.090 | 47 (55) | 0.673 |
| ≥ 4 days (n = 41) | 24 (59) | 0.328 | 27 (66) | 0.805 |
| Same day (n = 31) | 22 (71) | Ref. | 19 (61) | Ref. |
| Day of last backwash | ||||
| Weekday (n = 138) | 77 (56) | 0.333 | 82 (59) | 1.000 |
| Weekend (n = 19) | 13 (68) | Ref. | 11 (58) | Ref. |
| Characteristic . | PCR positive for E. coli (N = 93)an (%) . | p-valueb . | PCR positive for P. aeruginosa (N = 95)an (%) . | p-valueb . |
|---|---|---|---|---|
| Location | ||||
| Outdoor (n = 104) | 60 (58) | 1.000 | 67 (64) | 0.067 |
| Indoor (n = 57) | 33 (58) | Ref. | 28 (49) | Ref. |
| Setting | ||||
| Municipal (n = 37) | 26 (70) | 0.048 | 22 (59) | 0.843 |
| Waterpark (n = 35) | 23 (66) | 0.114 | 18 (51) | 0.316 |
| Membership/Club (n = 89) | 44 (49) | Ref. | 55 (62) | Ref. |
| Primary patron designation | ||||
| Primarily children (n = 15) | 11 (73) | 0.274 | 10 (67) | 0.595 |
| Adults and children (n = 145) | 81 (56) | Ref. | 85 (59) | Ref. |
| Stabilized chlorine usage | ||||
| No (n = 90) | 53 (59) | 0.751 | 51 (57) | 0.522 |
| Yes (n = 71) | 40 (56) | Ref. | 44 (62) | Ref. |
| Time since last backwash | ||||
| 1–3 days (n = 85) | 44 (52) | 0.090 | 47 (55) | 0.673 |
| ≥ 4 days (n = 41) | 24 (59) | 0.328 | 27 (66) | 0.805 |
| Same day (n = 31) | 22 (71) | Ref. | 19 (61) | Ref. |
| Day of last backwash | ||||
| Weekday (n = 138) | 77 (56) | 0.333 | 82 (59) | 1.000 |
| Weekend (n = 19) | 13 (68) | Ref. | 11 (58) | Ref. |
Note: Denominators might vary slightly due to missing values.
aCycle threshold (Ct) value <40 was considered a positive result.
bFisher's exact test.