INFECTION PREVENTION
0.1-0.5 microns 0.5-0.7 microns 0.7-1 microns 1-2 microns 2-5 microns 5-10 microns
BSRMA (CFU per cm2 Cultures
)
Control 5,788 2,928 1,847 612 5 3
48,549
S. aureus E. coli
APO
4,286 1,865 992 631 77 18
31,662
S. aureus E. coli
PS
5,218 2,248 1,637 603 6 3
42,569
S. aureus E. coli
APO + PS 4,242 2,259 1,326 557 19 4
37,898
S. aureus E. coli
Table 1. Results of air particle count samples (APCs), bacteria specific rapid metabolic assays (BSRMA) and cultures in all rooms prior to any intervention.
0.1-0.5 microns 0.5-0.7 microns 0.7-1 microns 1-2 microns 2-5 microns 5-10 microns
BSRMA (CFU per cm2 Cultures
)
Control 3,030 2,496 1,310 405 5 2
38,352
S. aureus E. coli
Table 2. Results after four weeks.
0.1-0.5 microns 0.5-0.7 microns 0.7-1 microns 1-2 microns 2-5 microns 5-10 microns
BSRMA (CFU per cm2 Cultures
)
Control 3,083 1,517 1,004 353 6 3
37,189
S. aureus E. coli
Table 3. Results after ten weeks. In the rooms with the PS disinfecting
technology, the surfaces were treated after the first set of samples were taken. Treatment was done by spraying the solution onto the surfaces, they were then allowed to dry fully before students were allowed to enter the rooms. The APO units were placed at the back of the rooms away from the entry doors, after the first set of baseline samples were taken. They were activated at level three which is the manufacturer’s recommendation for rooms of the size to be treated. A notice saying, ‘do not turn off’ with no explanation of what the units were doing, was taped to each of the units. Surfaces sampled, were comprised of similar materials, allowing for maximum potential to gain comparator results. Whilst standard testing requires samples
to be taken from 10cm2 areas, evidence
has shown that on surfaces where BSRMA live CFU counts are low, culture rarely shows any result.4,7,11
There is therefore
a much beter chance of geting a result from the larger sample area 20cm2
Surface samples were , which
is in fact four times the size of a standard sample area.2,8,11
taken from two areas in each room using sterile Dacron swabs dampened with Aespetol. BSRMA counts were used to determine ‘true’ levels of live bacterial contamination to within 10 CFUs. Blood agar plate cultures were used for bacterial species identification using the same samples.13
from 20cm above both 20cm2
Twenty air samples were taken areas, on
flat tabletops using a multiple particle sampler unit. An average was calculated between the 240 samples of air and the 48
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APO 1,353 298 108 44 56 16
4,065 None
PS
1,849 182 147 198 11 4
2,403 None
APO + PS 794 139 124 173 27 9
2,222 None
APO 1,124 463 290 166 36 18
6,629 None
PS
932 137 189 106 6 4
2,975 None
APO + PS 671 128 118 80 9
18
2,526 None
BSRMA swabs, to give an overall average of air particles and surface CFU counts within the room at each data point.7
culture samples were processed at room temperature (21-23°C).13,14
Results/data sub-sectional study Tables 1 to 3 show the averaged results of air sampling by particulate size, the averaged BSRMA results CFU per cm2
,
and the result of cultures. From air particle and BSRMA testing, there were no individual sample results of note, all were within statistical relevance of the partner tests.
Figures from the tables clearly show
a significant reduction in CFU counts per 20cm2
, and air particle counts by size in
the treated rooms. No cultures grew post treatment with either APO or PS in all the treated rooms. The cultures that produced results from the pre-treatment samples grew predominantly Staphylococcus aureus and Escherichia coli, therefore, the air particle counts of most interest are the 0.5-0.7 microns and 0.7-0.1 microns combined (see Table 4). This allows us to directly compare the relationship of the total of these two size ranges, with the CFU results from the surface BSRMA samples. When all the 8,400 AP sample
results from the wider full study were analysed against the 740 BSRMA results, the average combined APC to CFU relationship was found to be 9.57 APs to 100 CFUs, with a range of 8.11 APs to 13.69 APs to 100 CFUs. Further analysis shows that in the
control room, the bacterial counts in the air have an average ratio of 9.36 air particles to 100 CFUs when compared to surface CFU counts. There was no statistical difference between
in air counts of VOCs or CO2
any of the rooms, including the control room. There were no changes after any antimicrobial treatments of the air or surfaces, showing there is no relationship between CO2
levels and either actual air
or actual surface contamination after treatment with these highly effective antimicrobials. It is worthy of note, that no cultures
grew on samples where BSRMA results were below 75 CFUs per cm2
, or with
a combined 0.5-1 micron APC of 2,521 particles.
Conclusions As a result of this study, it is now the opinion of the authors that there is a clear relationship between air and surface contamination in both directions. Most importantly, as we can now determine that surface CFU counts will be approximately ten times greater than air counts between 0.5 and 1 microns, it is
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