TABLE 1.
Estimated LOD by surface material and sampling method
| Surface | Method | No. of runs | No. of samples | LODa
|
|||
|---|---|---|---|---|---|---|---|
| CFU/100 cm2
|
CFU/sampled areab
|
||||||
| LOD95 | 95% CI | LOD95 | 95% CI | ||||
| Steel | Swabc | 9 | 107 | 190 | 74-3,700 | 200 | 76-3,800 |
| Wiped | 10 | 90 | 15 | 7.6-84 | 140 | 71-780 | |
| Vacuumd | 10 | 90 | 44 | 24-140 | 410 | 230-1,300 | |
| Carpet | Swab | 9 | 108 | 40 | 16-560 | 41 | 17-580 |
| Wipe | 10 (9)e | 90 (81) | 9.2 (9.9) | 1.8-2.7 × 1031f (4.6-760) | 85 (92) | 17-2.5 × 1032f (42-7,100) | |
| Vacuum | 10 | 90 | 28 | 14-130 | 260 | 130-1,300 | |
The LOD, defined here as the lowest concentration that could be detected (i.e., positive for CFU) with LOD95, was estimated using probit regression (SAS PROBIT procedure), and 95% CIs were estimated using Fieller's procedure (15).
The sampled surface areas were approximately 103 cm2 for the swab method and 929 cm2 for the wipe and vacuum methods.
Steel-swab combination results exclude a single sample with contaminant overgrowth.
The steel-wipe and steel-vacuum combinations required 3 or more CFU for a positive result (see text for details); all other surface-method combinations required 1 or more CFU for a positive result.
The carpet-wipe combination CI was very wide, likely due to the results of a single run in which 100% of the wipe samples were positive in spite of the very low surface loading; results excluding this run are in parentheses.
The 95% CI for the carpet-wipe combination could not be computed due to constraints imposed by Fieller's method; results shown have 94% confidence rather than 95% confidence.