Table 3.
Statistical analysis of positivity rates for various bacterial species or groups stratified by preincubation time.
| PI | N (%) | Chi-Sq | CATT | OR (95% CI) | P value | OR/h (95% CI) |
|---|---|---|---|---|---|---|
| BHS | ||||||
| < 5 h | 401 (5.41) | 0.0807 | 0.0239 | 1 |
1.02 (1.00–1.03) P = 0.0650 |
|
| 5–10 h | 106 (6.87) | 1.29 (1.03–1.61) | 0.0244 | |||
| 10–20 h | 54 (6.62) | 1.24 (0.92–1.66) | 0.1543 | |||
| > 20 h | 13 (6.95) | 1.30 (0.74–2.31) | 0.3616 | |||
| S. aureus | ||||||
| < 5 h | 1243 (16.79) | 0.004 | 0.006 | 1 |
0.99 (0.98–1.00) P = 0.0468 |
|
| 5–10 h | 219 (14.20) | 0.82 (0.70–0.96) | 0.0126 | |||
| 10–20 h | 131 (16.05) | 0.95 (0.78–1.15) | 0.5937 | |||
| > 20 h | 17 (9.09) | 0.50 (0.30–0.82) | 0.0062 | |||
| E. coli | ||||||
| < 5 h | 1467 (19.81) | < 0.0001 | < 0.0001 | 1 |
1.04 (1.03–1.04) P < 0.0001 |
|
| 5–10 h | 321 (20.82) | 1.06 (0.93–1.22) | 0.3701 | |||
| 10–20 h | 236 (28.92) | 1.65 (1.40–1.94) | < 0.0001 | |||
| > 20 h | 65 (34.76) | 2.15 (1.59–2.93) | < 0.0001 | |||
| CoNS | ||||||
| < 5 h | 1013 (13.68) | 0.0007 | 0.0007 | 1 |
0.97 (0.96–0.99) P = 0.0001 |
|
| 5–10 h | 211 (13.68) | 1.00 (0.85–1.17) | 0.9986 | |||
| 10–20 h | 72 (8.82) | 0.61 (0.48–0.79) | 0.0001 | |||
| > 20 h | 19 (10.16) | 0.71 (0.44–1.15) | 0.1672 | |||
| Entero-coccus spp | ||||||
| < 5 h | 497 (6.71) | 0.4658 | 0.113 | 1 |
0.99 (0.97–1.00) P = 0.0872 |
|
| 5–10 h | 95 (6.16) | 0.91 (0.73–1.15) | 0.428 | |||
| 10–20 h | 45 (5.51) | 0.81 (0.59–1.11) | 0.1916 | |||
| > 20 h | 10 (5.35) | 0.79 (0.41–1.49 | 0.4616 | |||
| K. pneumoniae | ||||||
| < 5 h | 363 (4.90) | 0.1493 | 0.0845 | 1 |
1.01 (0.99–1.02) P = 0.4418 |
|
| 5–10 h | 94 (6.10) | 1.26 (1.00–1.59) | 0.0532 | |||
| 10–20 h | 50 (6.13) | 1.27 (0.93–1.72) | 0.1292 | |||
| > 20 h | 9 (4.81) | 0.98 (0.49–1.93) | 0.9551 | |||
| VGS/ANG | ||||||
| < 5 h | 337 (4.55) | 0.1056 | 0.3110 | 1 |
0.98 (0.96–1.01) P = 0.1461 |
|
| 5–10 h | 83 (5.38) | 1.19 (0.93–1.53) | 0.161 | |||
| 10–20 h | 27 (3.31) | 0.72 (0.48–1.07) | 0.103 | |||
| > 20 h | 6 (3.21) | 0.70 (0.31–1.58) | 0.3851 | |||
| S. pneumoniae | ||||||
| < 5 h | 179 (2.42) | 0.1280 | 0.6289 | 1 |
1.00 (0.97–1.02) P = 0.8620 |
|
| 5–10 h | 49 (3.18) | 1.32 (0.96–1.83) | 0.0859 | |||
| 10–20 h | 16 (1.96) | 0.81 (0.48–1.35) | 0.4166 | |||
| > 20 h | 2 (1.07) | 0.44 (0.11–1.77) | 0.2462 | |||
| Other coliforms | ||||||
| < 5 h | 472 (6.37) | 0.0922 | 0.0190 | 1 |
1.02 (1.01–1.03) P = 0.0058 |
|
| 5–10 h | 102 (6.61) | 1.04 (0.83–1.30) | 0.7266 | |||
| 10–20 h | 68 (8.33) | 1.34 (1.02–1.74) | 0.0327 | |||
| > 20 h | 17 (9.09) | 1.47 (0.88–2.44) | 0.1375 | |||
| NF | ||||||
| < 5 h | 166 (2.24) | 0.1450 | 0.5999 | 1 |
0.99 (0.96–1.02) P = 0.4570 |
|
| 5–10 h | 27 (1.75) | 0.77 (0.52–1.17) | 0.2285 | |||
| 10–20 h | 23 (2.82) | 1.27 (0.81–1.97) | 0.298 | |||
| > 20 h | 1 (0.53) | 0.23 (0.03–1.68) | 0.1492 | |||
P values for Chi-square and the Cochran-Armitage trend test are shown. Logistical regression analysis was performed both with stratified preincubation times, using the < 5 h preincubation group as reference, and using time as a continuous variable. Statistically significant results are bolded. PI: preincubation, CI: confidence interval, Chi-sq: Chi-square, CATT: Cochran-Armitage Trend Test, OR: odds ratio. N: number of isolates, BHS: beta-hemolytic Streptococcus, CoNS: coagulase-negative Staphylococcus, VGS/ANG: viridans group Streptococcus and S. anginosus group, Mn: mean, NF: non-fermenting gram negative bacilli, TOT: total.