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Due to the intricacy of the process, publishing and validating new international norms and regulations adapted to novel technologies is a notoriously slow development. For a very long time, the virtually only adapted norm to test the efficacy of airborne disinfection systems (automated or not) was the AFNOR-published NF T 72-281, from France. For this reason, this standard was used as the base for the new European norm EN 17272, which after a few years of preparation, was then given the status of national standard across the European Union in October 2020. This new norm, entitled Chemical disinfectants and antiseptics – Methods of airborne room disinfection by automated process – Determination of bactericidal, mycobactericidal, sporicidal, fungicidal, yeasticidal, virucidal and phagocidal activities, is now the golden standard for evaluating efficacy of automated room disinfection systems such as the STERISAFE PRO. A few changes were made from the original AFNOR documents, and manufacturers are now asked to test their products only according to EN 17272 and to update their previous results obtained through NF T 72-281 to the new norm.

 

Common grounds and general concepts

Efficacy tests are generally based on the same principle, and both NF T 72-281 and EN 17272 are no exceptions. Microorganisms are counted as numbers of colony forming units (CFUs), and efficacy is given as the difference between the CFU count before and after application of the disinfecting agent. The result is given as a “log reduction”, where a log reduction of 1 corresponds to a 10-fold reduction. For example, for a 106 initial CFU, a log reduction of 4 would see a reduction to 102 CFU after treatment. This is typically marked on commercial packaging as a kill-rate percentage, where a 2-log reduction corresponds to a 99% germicidal power, a 3-log to 99.9%, and so forth.

Both standards also give the surrogate microorganisms and strains that must be tested. Typically, those strains are chosen to be representative of families or types of common pathogens. In addition to be divided in categories (bacteria, viruses, spores, fungi and yeasts, bacteriophages and mycobacteria), required testing will also depend depending on the intended area of use. Three areas are recognized by both norms: medical, veterinary and general (food, industrial, domestic and institutional) areas. For example, Mycobacterium avium, a significant pathogen for livestock and wildlife, is only required to be tested against for biocides intended in the veterinary area.

 

Distribution test: a welcome addition

 

Arguably the most important change made for EN 17272 as compared with NF T 72-281 is the requirement to pass a “distribution test”. While NF T 72-281 was widely accepted as a semi-field method replicating real-life situations, EN 17272 goes a step forward in its requirements. Whereas the older standard demanded microorganism sample discs to be placed at a single location, at a certain distance from the biocidal device, the new version requires several sample locations in a bid to assess the distribution of the active agent.

This is potentially a game-changer in the world of automated room disinfection systems, as lesser-performing devices were notorious for having a more limited range of distribution with often inconsistent results. Under the previous norm, this flaw could be partially circumvented by directing the biocidal flow toward the sample discs. By following EN 17272, the systems that are more likely to pass such a test will be limited to more effective devices based on gas diffusion or chemical vaporisation, as opposed to aerosolization-based technologies.

The required organisms used for the EN 17272 distribution test is Staphylococcus aureus, a common bacterium often involved in opportunistic infections. To pass this test, the tested device must show an efficacy of at least log-5 reduction for each of the eight sample discs placed at every corner of the test room.

 

Real-life settings distribution tests

In addition to EN 17272-mandated tests, STERISAFE PRO has been used in other distribution tests for peer-reviewed scientific articles. Professor Johannes Knobloch and his research group, from the Institute for Medical Microbiology, Virology, and Hygiene at the Medical Center Hamburg-Eppendorf (UKE) recently published an article using this method, as a mean to compare two Automated Room Disinfection (ARD) technologies. The article and its summary can be found here: Best in test – Comparison of STERISAFE PRO and Aerosolized Hydrogen Peroxide.

 

Other changes

In terms of required test microorganisms, EN 17272 also saw the addition or reclassification of some surrogate strains. For example, to reflect its increased importance in healthcare-associated infections (HAIs), the pathogen Acinetobacter baumanii was added to the list of required test bacteria for the healthcare area of use, while Pseudomanos aeruginosa  is now only needed for the veterinary and general areas. Similarly, Proteus hauseri and porcine parvovirus were added as requirements for veterinary usage.

Also, to acknowledge the dangerosity of spores in the healthcare industry, the minimal accepted efficacy threshold for Bacillus subtilis spores was increased to 4-log reduction, while in the two other areas of use the passing grade was maintained at 3-log reduction.

Other changes include the substitution of skimmed milk by bovine serum albumin (BSA) as the sole accepted interfering substance for clean conditions; minor tweaking of obligatory conditions of relative humidity (from 40-80 %RH to 50-75 %RH, unless specified otherwise); and the removal of some informative sections, notably concerning disinfection using UV technology.

STERISAFE and EN 17272

Since its inception, STERISAFE has been proud to uphold its products to the highest standards and to scrupulously follow the most stringent and adapted norms, always according to European legislation. With the publication of EN 17272, this vision will not change, and STERISAFE is currently in the process of updating all efficacy results obtained through NF T 72-281, as well as conducting the additional tests needed.

 

References

  1. L’Association Française de Normalisation (2014). NF T 72-281. Procédés de désinfection des surfaces par voie aérienne – détermination de l’activité bactéricide, fongicide, levuricide, mycobactéricide, tuberculocide sporicide et virucide incluant les bactériophages. Paris: AFNOR
  2. European Committee for Standardization (2020). EN 17272. Chemical disinfectants and antiseptics – Methods of airborne disinfection by automated process – Determination of bactericidal, mycobactericidal, sporicidal, fungicidal, yeasticidal, virucidal and phagocidal activities. Brussels: CEN