INFECTION PREVENTION
now possible to use a simple air particle sampler 20 cm above a surface to get a reading accurate enough to approximate surface contamination in just a few minutes, allowing us to sample areas of highest contamination for species identification. Whilst it is clear from Table 4, that
there are pathogens of a different particle size to those used for an APC to CFU ratio, only nine out 840 culture plates produced cultures with species other than S. aureus and E. coli. In practice, these culture results should not be ignored as they may indicate the need for specialist disinfectants, or change of standard disinfectants due to the emergence of a resistant species. In the sub-sectional study looking at
the two new disinfecting technologies, as the only measurable differences between the study rooms where the interventions undertaken with both the APO and PS technologies, it is not unreasonable to conclude that these interventions were responsible for the changes. Although this remains an inexact
science, the relationship of approximately 10:1 significant air particles to CFU levels, is easy to understand and utilise as a measurement for infection control staff. A simple one minute air sampling test taken 20cm above a surface, showing a result
in the 0.5 to 1 micron range, will give a reasonable estimate of 10 times that amount of CFUs. If the result shows more than 2,500 APCs in total in that range, there is a high expectation that with a good technique, a culture sample will give a species identification result. This now gives us a test methodology that fulfils all four of the original requirements for us to begin to gather enough data to make recommendations as to the safe levels of bacterial surface contamination. Until there is a consensus on what are
considered (or proven to be) acceptable levels of surface/air contamination, the approximation of 10:1 ratio is sufficient to change practice in our hospitals. It may now be possible to re clean areas that disinfectants have been ineffective on, and to potentially see the build-up of disinfectant resistance before cross- infection problems occur. This would increase the speed that IPC teams have the evidence needed to change disinfectant chemistries based on results of air samples, whilst they wait for culture or PCR results from laboratories. In the sub-sectional study, although
there was a measurable difference in surface counts using the BSRMA tests, as there were no cultures grown in either of the three treated rooms after treatment, it
Species
Staphylococcus aureus Pseudomonas spp.
Size (microns) 0.52
0.55 - 0.7
Streptococcus pneumoniae 0.5 - 1.25 Klebsiella spp.
Haemophilus influenzae Shigella spp.
Escherichia coli
Clostridium perfringens Campylobacter spp. Bacillus cereus
0.5 - 0.8 0.3 - 1
0.4 - 0.6 0.6 - 0.7 3 - 4 1.7
3 - 4
Table 4. Approximate particle sizes of pathogens of interest to the study.
is impossible to know how much difference in potential for cross contamination there is from either surfaces or air. It is of course possible that due to the ‘Holism’ or ‘Entourage theory’ that the individual product efficacy is increased by the combined use with the other product.14
As
such, it is the authors’ opinion that the most effective way to use the technologies is by combining them. Results also show, air sampling requires a total of more than 2,500 particles in the 0.5-1 micron range to produce a culture plate result from a surface swab. Air sampling could
April 2026
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