Fig 1.
Pictorial overview of the sampling methods used in the study.
Single medium single-pass discrete (SP-Discrete); single medium multi-pass discrete (MP-Discrete); single medium, single-pass composite (SM-SPC); single medium, multi-pass composite (SM-MPC); and multi-medium, multi-pass composite (MM-MPC) were used in the study. Buffer; Phosphate buffered saline containing 0.02% Tween 80.
Fig 2.
Pictorial overview of the sample process and analysis method for each sampling sponge.
*For sponges used with the multi-medium multi-pass composite (MM-MPC) method, each of the sponges used for sampling were extracted one at a time, in the same 90 mL buffer. #The volume following extraction was >90 mL (up to 105 mL) for MM-MPC samples; therefore, the sample was split into three aliquots prior to being combined. ‡The final target volume for all methods was 6 mL, including the MM-MPC method.
Table 1.
The six experimental factors used in the study to evaluate recovery efficiency.
Fig 3.
Pictorial overview of the test design used to compare the single media single pass composite (SM-SPC) method with the single media multi pass composite (SM-MPC) method.
Each method was tested using 4 or 8 locations composited. On one test day, all locations for all tests were contaminated. On the other test day, only one random location was contaminated. Gray Sponge: Negative Process Control. Each square represents an individual coupon location. Green: SM-SPC method with 4 coupons; Purple: SM-MPC method with 4 coupons; Light Blue: SM-SPC method with 8 coupons; Dark Blue: SM-MPC method with 8 coupons; Yellow: SP-Discrete serving as process control for the SM-SPC; Orange: MP-Discrete serving as process control for the SM-MPC; Red: Negative control coupon.
Table 2.
ANOVA results showing statistical significance for the tested factors and their interactions for clean coupon materials.
Fig 4.
Coupon material and compositing methodology are significant experimental factors on the response variable, recovery efficiency.
Of the materials tested, ceramic tile and stainless steel had the highest recovery efficiency and vinyl tile had the lowest RE. For all materials and CFU targets tested (10, 25, 50, 100 CFU), the MM-MPC method yielded higher RE than the SM-MPC method. The process controls, MP-Discrete, data are included for comparative purposes. C = ceramic; D = drywall; S = stainless steel; V = vinyl tile.
Fig 5.
The composite methodology is significant, and the MM-MPC method yields the highest RE when considering the number of locations composited and number of coupons contaminated.
The four scenarios tested were 4 samples composited with (A) all or (B) one random coupon contaminated and 8 samples composited with (C) all or (D) one random coupon contaminated. The process control, MP-Discrete, data is included for comparative purposed for the composite methods.
Fig 6.
The interaction of two experimental factors, CFU target and number of contaminated locations, significantly affect recovery efficiency (p = 0.0271).
The means are plotted as open circles and the error bars are representative of two standard deviations.
Table 3.
ANOVA results for experiments with 16 locations composited using the MM-MPC method.
Fig 7.
Increasing the number of locations composited from 8 to 16 does not reduce RE.
The experiments were conducted using the MM-MPC methodology with 1, 4, 8, or 16 locations composited. The data for ceramic and stainless steel coupons are provided together in the MP-Discrete data set.
Table 4.
ANOVA results show that the presence of grime and the interaction between coupon type and grime presence are significant for RE.
Fig 8.
Grime coating on coupons is associated with an increased RE for stainless steel and vinyl coupons, but RE is reduced when grime is present on ceramic coupons.
The presence of grime is an independent significant factor on RE. The interaction between material type and grime presence is also significant for RE.
Fig 9.
The FNR for the MM-MPC and MP-Discrete methods are similar for grime coated and clean coupons.
The highest FNR were associated with the SM-MPC method. FNR decreases as CFU increases, and is consistently lowest at 100 CFU for ceramic (A), stainless steel (B), and vinyl (C) surfaces that are either clean or grime coated. The gray line in each plot demarcates the 0.1 FNR threshold (i.e., LOD90). The CFU targets used were 5, 10, 25, 50, and 100 CFU per coupon. Coupons were contaminated in four or eight locations for the SM-MPC and MM-MPC methods.
Fig 10.
Limit of Detection (LOD90) is lower using the MM-MPC method for each coupon material compared to the SM-MPC method.
The CFU targets used were 5, 10, 25, 50, and 100 CFU per coupon. Coupons were contaminated in four or eight locations for the both composite methods.