TABLE 3.

Precision and mean estimated surface concentration by surface material, target concentration, and sampling method

Surface	Targeta	Method	Precision CV(%)b				Concn (CFU/100 cm2)c
			CVR	CVL	CVW	CVmethod	No.	Mean	95% CI
Steel	Low (3 runs)	Reference agar	5.6		230		48	8.3	0-20
		Swab	0	110	460	470	36	0.12	0-1.4 A
		Wipe	0	8.5	200	200	27	2.3	1.1-3.6 AC
		Vacuum	50	38	98	100	27	0.43	0-1.7 C
	Medium (3 runs)	Reference agar	19		30		48	38	19-57
		Swab	27	0	82	82	36	2.5	0-6.5 A
		Wipe	28	27	76	80	27	8.4	5.0-12 AC
		Vacuum	0	18	82	84	27	1.8	0-5.2 C
	High (3 runs)	Reference agar	30		19		48	270	65-480
		Swab	87	19	75	78	35	15	0.47-29 A
		Wipe	45	25	61	66	27	50	36-64 AC
		Vacuum	5.8	35	82	89	27	10	0-24 C
Carpet	Low (2 runs)	Reference agar	34		190		32	1.8	0-11
		Swab	0	85	220	230	24	0.18	0-1.1 A
		Wipe	0	26	180	180	18	1.7	0.80-2.7 AC
		Vacuum	0	0	170	170	18	0.11	0-1.1 C
	Medium (4 runs)d	Reference agar	0		97		64	17	10-23
		Swab	98	0	73	73	48	2.3	0-5.7 B
		Wipe	52	9.3	100	100	36	3.4	0.14-6.8 C
		Vacuum	57	0	110	110	36	0.61	0-3.9 BC
	High (3 runs)	Reference agar	62		26		48	190	0-470
		Swab	40	21	57	61	36	18	0-64 AB
		Wipe	47	8.6	37	38	26	35	0-77 AC
		Vacuum	37	30	44	53	27	6.2	0-48 BC

^aTarget deposition densities were approximately 3, 30, and 200 CFU/100 cm² for low, medium, and high, respectively.

^bPrecision (CV) was estimated using the MIXED procedure in SAS. The model for reference agar included a random effect for chamber run resulting in between-run (σ²_B) and within-run (σ²_W) variance components. Separate models for each of the sampling methods included random effects for chamber run and laboratory resulting in between-run (σ²_B), between-lab (σ²_L), and within-lab (σ²_W) variance components. For each source of variation, CV = 100% × [(σ²_source)^½/Mean], so CV_R is the between-run CV, CV_L is the between-lab CV, and CV_W is the within-run (agar) or within-lab (sampling methods) CV. For the sampling methods, CV_method incorporates both between-lab and within-lab variability.

^cMeans and 95% CIs were estimated using the MIXED procedure in SAS. The model for reference agar included a random effect for chamber run. The model for the sampling methods included random effects for chamber run and laboratory and fixed effects for mean agar and method. Means for sampling methods with the same letter are significantly different (Tukey-Kramer adjusted P value of <0.05).

^dA single carpet run was intended to be low but was considered to be medium based on the agar results.