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Misting hypochlorous acid in communal spaces – case study

Misting hypochlorous acid in communal spaces – a case study

BACKGROUND

The aim of this project was to assess the decontamination efficacy of misting hypochlorous acid brand Salvesan applied as a mist in communal spaces of a working food factory. Salvesan is a fast acting biocide based on hypochlorous acid (HOCl). Assessing efficacy was achieved by measuring micro bioburden on hand-touch surfaces / the environment before and after the misting process. Misting was achieved using a high-pressure sprayer provided by Aqualution / Air Pumping. The mist particles are typically 4-5 microns in diameter which allows the mist to float freely in the air (rather than drop quickly) and also prevents wetness on floors / surfaces.

 

THE TRIAL

The trial was carried out in four communal areas of the factory: canteen, handwashing area (pre entrance to the packing hall), female WCs and male WCs. We investigated decontamination rates on a range of surfaces immediately after environmental misting with Salvesan. Surfaces of different materials were chosen. The majority of the surfaces (22 of the 28) were hand touch sites; three of the remaining surfaces were floors (to give a worst case scenario) and the reservoirs of hand dryers (as they potentially harbour significant biofilm).

The site was asked not to clean the area prior to our arrival to ensure that it was well trafficked and had sufficient levels of microbial contamination. Sampling sites were chosen across a range of surfaces in the chosen areas. The areas were light, warm and visually clean.

All samples were taken using sterile trans-swabs. Sampling sites were fitted with temporary templates (area c 100cm2) to ensure that pre and post treatment swabbing areas were the same. Some sampling sites were not sufficiently large to accommodate a template so they were swabbed free hand.

Misting took 4-10 minutes depending on the size of the area. This was followed by a 5 minute dwell time. The same areas were then re-swabbed by the same person using the same technique.

 

THE RESULTS

Mean, median and mode results for all sampling sites

 

Pre (cfu)Post (cfu)Pre LogPost LogLog reduction% cfu reduction
Mean4,121,6472,177,53952399.9
Median230,000<1050599.999
Mode10,000,000<1070799.99999

 

The numerical average reductions appear to be unremarkable. However, once log transformed there is an average 3 log reduction (ie 99.9% of bacterial burden is removed through the misting process). The median figure pre misting was 230,000 cfu per swab. After misting it was <10 which represents a 5 log reduction. The most frequently observed result (mode) pre misting was 10,000,000 per swab (11 observations) and after misting was <10 cfu per swab (15 observations).

 

Mean, median and mode results for all hand touch sites

 

Pre (cfu)Post (cfu)Pre LogPost LogLog reduction% cfu reduction
Mean3,826,178497,50441399.9
Median97,500<1050599.999
Mode10,000,000<1070799.99999

 

The trends are very similar when looking solely at hand touch sites, though the median pre counts were, as expected, slightly lower when the floors were excluded. Again the most commonly observed pre-treatment count was 10,000,000 cfu per swab (8 observations, 36%) and the most commonly observed post treatment count was <10 cfu per swab (15 observations, 68%). The veneer cubicle door and stainless steel lock mechanisms in both the female and male WC were all 10,000,000 cfu prior to treatment and all <10 cfu after treatment.

Misting Salvesan hypochlorous acid conferred a median 5 log reduction on surface bacteria on hand touch sites ie 99.999% of bacteria were removed by the treatment.

There are no standard acceptable levels of surface bioburden for hand touch sites in hospitals. However, proposals of <2.5cfu/cm2 have been proposed by NHS researchers / clinicians. This equates to 250 cfu/swab. Of the 22 hand touch areas chosen, 77% failed this criteria prior to misting. After misting hypochlorous acid 73% of sites passed (with 94% of those passes achieving results of <1 cfu/swab). This pass rate would be even greater if the Salvesan was used as a disinfection step after a traditional detergent clean.

 

MISTING HYPOCHLOROUS ACID CONCLUSIONS

Misting Salvesan hypochlorous acid resulted in a significant and repeatable effect on surface log counts achieving 5 log (99.999%) median reductions. Modal figures suggested a 7 log reduction ie 99.99999% of surface bacteria were removed.

Surface bioburden was <1 cfu/cm2 on 73% of hand touch surfaces after misting. The high pressure air system is suitable for applying Salvesan in a range of environments (ambient and chilled) and its high output rate means it can treat large areas efficiently and quickly.

Click here for the full lab report.

For more case studies see:

NHS HOSPITAL SALVESAN MISTING CASE STUDY

SALVESAN BUS DISINFECTION TRIAL VIA AN AUTOMATED DELIVERY SYSTEM

SALVESAN FOGGING USED FOR COVID-19 INFECTION CONTROL IN UK’S LEADING FLOWER FACTORY