Statistical Analyses PFUs from all experiments (persistence and simulation) were converted to log10 and the survival rate curve was constructed using Microsoft Excel. The transfer rate is defined as: log PFU/cm 2 on recipient surface divided by log PFU/cm 2 on the original surface (source) multiplied by 100.
TABLE 2
Transfer Rate of Phi 6 From Food Contact Surfaces (Stainless Steel, Tabletop, and Countertop) to Wiping Tools (Sponge and Microfiber Towel) and Hands
Log and Transfer Rate With Low Level Inoculation (10 3 PFU/cm 2 )
Surface
Log and Transfer Rate With High Level Inoculation (10 7 PFU/cm 2 )
Results and Discussion
Log PFU/cm 2
Transfer Rate b (%)
Transfer Rate (%)
Log PFU/cm 2 a
Persistence of Phi 6—Food Service Fomites
Stainless steel to sponge
2.3 ± 0.3
38
0.7 ± 0.5
35
Table 1 shows the persistence of phi 6 on sponges, microfiber towels, stainless steel, wooden floors, tabletops, countertops, cut- ting boards, and light switches over a period of 30 days. The results indicate that phi 6 can persist for as long as 13 days on the follow- ing coupons: sponges, tabletops, countertops, cutting boards, and light switches. In addi- tion, phi 6 persisted for as long as 10 days on microfiber towel and wooden floor coupons. Rapid reductions of phi 6 were observed within the first 2 days for all fomites, where reductions of more than 2 logs PFU/cm 2 were recorded on all surfaces except sponges and countertops. After day 2, the reductions of the phi 6 levels remained constant until day 13, at which point phi 6 fell below the detec- tion limit of 0.9 logs PFU/cm 2 for all surfaces. Previous literature has shown that food and food contact surfaces in food service operations could be a source for the cross- contamination and transmission of bacteria and viruses (Gibson et al., 2012). Santarpia et al. (2020) reported that a person infected with SARS-CoV-2 could contaminate the room environment where they were cared for—including air and environmental sur- faces such as personal items, room surfaces, and toilets. SARS-CoV-2 was also detected on food preparation surfaces, service areas, hos- pital isolation wards, air conditioning filters, sewage treatment units, and in air samples (Mouchtouri et al., 2020). These finding are significant because there is scientific evidence of potential viral transmission from contami- nated fomites to a person’s mouth (Rusin et al., 2002). Cross-Contamination of Phi 6— Surfaces Table 2 shows the transfer rate of phi 6 from food contact surfaces to wiping tools
Tabletop to sponge
1.8 ± 0.4 2.2 ± 0.1 1.6 ± 0.1
30 37 26
0.6 ± 0.3 0.9 ± 0.2 0.9 ± 0.3
30 45 45
Countertop to sponge
Stainless steel to microfiber towel Tabletop to microfiber towel Countertop to microfiber towel
1.7 ± 0.4
28
0.4 ± 0.2
20
2.1 ± 0.1
35
0.3 ± 0.3
5
Stainless steel to hand
2.4 ± 0.2 2.1 ± 0.3 2.2 ± 0.1
40 35 37
0.5 ± 0.3 1.2 ± 0.1 0.6 ± 0.3
25 60 30
Tabletop to hand
Countertop to hand
a Mean and standard deviation of phi 6 from the inoculated stainless steel, tabletop, or countertop (10 7 or 10 3 PFU/cm 2 ) to sponge or microfiber towel when used to wipe each surface, or to hands when hands touched each surface for 20 s ( N = 6). b The transfer rate (percentage) of mean and standard deviation of phi 6 from the inoculated stainless steel, tabletop, or countertop (10 7 or 10 3 PFU/cm 2 ) to sponge or microfiber towel when used to wipe each surface, or to hands when hands touched each surface for 20 s ( N = 6).
els, sprayed with 70% ethanol, and allowed to air-dry. The index finger (primary transfer) of each hand was used to touch the contami- nated surfaces for 20 s. Samples from hands were collected using a glove-juice method (Larson et al., 1980; Sirsat et al., 2013) with brief modifications as detailed. The index finger from each hand that touched the con- taminated surfaces for 20 s was placed in a sterile surgical glove containing 1 ml of ster- ile 0.02% PBST virus buer in the index fin- ger section. Next, the finger with the glove on was vortexed for 60 s. The sample was then transferred from the glove index finger region to a sterile 10-ml conical tube using a sterile pipette; the sample then underwent further dilution and viability plate count analyses. Contamination of Cutting Boards and Hands With a High or Low Level of Phi 6 For the second scenario, cutting boards and hands were inoculated with 0.2 ml of phi 6
suspension (10 7 and 10 3 PFU/ml, respec- tively). Samples of produce (pepper, can- taloupe, and lettuce) were placed on an inoculated cutting board. After marking the portion of the produce that was placed on the cutting board, it was left in contact for 1 hr at room temperature (23 ± 2 °C). The marked (inoculated) portion of each produce sample was swabbed using an alginate cotton swab and placed into a tube containing 5 ml of 0.02% PBST. Additionally, produce sam- ples were placed in contact with inoculated hands for 1 min by touching marked portions of the produce. Next, 1 ml from each col- lected sample (after touching either cutting boards or hands) and 100 μl of overnight host were added to a tube containing 3 ml of TSA soft agar. The contents were shaken by hand, quickly poured onto TSA plates, allowed to solidify, and incubated for 24 hr at 22 °C. After the incubation period, PFUs were quantified.
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June 2023 • Journal of Environmental Health
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