Room disinfection by fogging

On the biocidal products market, we can observe a growing interest in preparations for disinfecting rooms by fogging.

The increasing popularity of this disinfection method is directly related to the publication of a standard by the European Committee for Standardization with the designation: 17272: 2020-10. The prevailing SARS-CoV-2 epidemic also contributed to the popularization of “fogging”. There is also a growing public awareness of the need to keep premises clean and sterile. This is particularly relevant for healthcare and teaching facilities, collective accommodation complexes, and for the wide range of veterinary area (including livestock buildings and animal transport procedures). Specialised laboratories offer these tests and can provide assistance in selecting the test range.


What is room disinfection by fogging?

Disinfection of rooms in an automatic process, also called fogging, consists in spraying a disinfectant in the form of steam, aerosol or gas. The disinfectant is usually dispersed by means of a specially adapted device, whose task is to administer the appropriate dose of the disinfectant per unit of time. However, this is not the rule, as manufacturers of chemical disinfectants are trying to eliminate the involvement of additional equipment. Moreover, they are working on single-use products or devices that spray aerosol under pressure directly from the container containing the product. Disinfection by fogging is a much more effective process than standard methods based on, for example, spraying the surface. That is because the aerosol produced in this way is able to reach all places in the room, and also significantly minimizes the risk of damage to the surface or equipment (e.g. medical equipment), for which too abundant and direct spraying of the disinfectant could be harmful. In addition, human involvement is also reduced due to the automation of the process.

Test procedure

Preliminary test

The preliminary test allows you to estimate the efficiency of the device in the test room. Depending on the purpose of use, the standard allows the test to be carried out in rooms up to 4 m³ (small rooms). The actual test is carried out in rooms with a cubature of 30 to 150 m³ (large rooms). The preliminary test should be performed under identical conditions to those used in the efficacy test. Regardless of the scope of examination chosen by the customer, the test strain should be Staphylococcus aureus. A reduction of the pathogen by a minimum of 5 logarithms allows the methodology to be considered validated. After achieving the required degree of reduction, proceed to the second stage, i.e. the efficacy test.

Efficacy test

The efficacy test, in simple terms, consists of placing test plates covered with a suspension containing the model organism at appropriate distances from the emitter. The placement of the test strains must comply with the requirements strictly defined in the EN 17272 methodology. Appropriate placement of the test strains enables the evaluation of the fogging efficiency against tested area. The next step is to spray the disinfectant in accordance with the manufacturer’s instructions for the device delivered for testing. The purpose of the “fogger” is to fill the entire cubature of the room with gas. The effectiveness of the device is also influenced by the disinfectant that is used in the process. What is more, a very important element is the synergy between the device and the biocidal preparation as it allows not only the efficiency of disinfection, acceleration of the process, as well as savings of the chemicals used. The disinfection process usually takes from several minutes to several hoursAfter the disinfection process is completed, laboratory technicians carry out tests and calculate the degree of reduction of a given pathogen in relation to the requirements of the standard. Afterwards, a comprehensive test report is prepared.

Biocidal preparations used in the fogging method

Chemical disinfectants used for fogging are usually developed in such a way that their harmfulness to the user and the disinfected surfaces is as low as possible. Another important element is the “ease” of airing the rooms after the process is finished. The most commonly used active substances are hydrogen peroxide, chemical compounds from the group of quaternary ammonium salts (e.g. benzalkonium chlorides). Also, compounds based on sodium hypochlorite or hypochlorous acid are popular, and the latter is gaining more and more popularity among biocidal product manufacturers as well as their customers. On the other hand, alcohol as an active substance in disinfection by this method occurs much less frequently.

Selection of the range of studies

The EN 17272 standard makes it possible to assess biocidal efficacy against bacteria, fungi, viruses, mycobacteria, spores and bacteriophages. The choice of the test range depends on the customer’s requirements and the area of application in which we intend to operate. In order to preserve the requirements of the methodology, tests confirming at least bactericidal and yeasticidal activity shall be carried out. Disinfection by fogging is used in the medical, veterinary, domestic and industrial/institutional areas (groups 2, 3 and 4 of category 1). The method was developed on the basis of the French standard AFNOR NF T72 281, which was replaced by a more recent equivalent in 2020.

Reference strains

Group II Medical area

In Group II, Category I of the classification of annex V of the Biocidal Products Regulation, we specify preparations for use in the medical area as well as outside the medical area. When confirming the bactericidal effectiveness in both situations, the basic test strains are P.aeruginosa, S.aureus, E.coli K12 and E.hirae. In addition, the client may wish to test for Salmonella, Legionella or, in the context of disinfection at >40°C for E.faecium. The fungicidal effectiveness in PT2 is confirmed on C.albicans and A.brasiliensis strains, sporicidal against B.subtilis, mycobactericidal against M. terrae and M.avium, and virucidal to the extent consistent with the declarations that the product should meet. Wirusami modelowymi mogą być: Feline calicivirus, Poliovirus type 1, Murine norovirus, Adenovirus type 5, Rotavirus, Vaccinia Virus, Human coronavirus 229E, wirusy grypy i inne. However, the use of disinfection at temperatures >40 °C requires tests confirming the effectiveness against the strain: Murine Parvovirus.

Group III Veterinary area

In this group, the bactericidal efficacy is tested with strains: P.aeruginosa, S.aureus, E.coli K12 and E.hirae. Possible optional strains are consulted directly with the entity requesting the tests, depending on the needs. Fungal strains are: C.albicans and A.brasiliensis, spores: B.subtilis and additionally B.cereus, mycobacteria: M.terrae, and the reference virus is: Bovine Enterovirus (BEV).

 Group IV Food and feed production area

The last product group where fogging devices for desinfection are used is group IV, i.e. the field of food and feed. In PT4 the bactericidal, fungicidal, sporicidal and virucidal efficacy is confirmed on the same pathogens as in group II. The exception is the mycobactericidal efficacy, the confirmation of which is not required. In the case of group IV, the phagicidal activity can be additionally determined. Selected strains of Phages are used to destroy pathogenic bacteria. The most common bacteria used to assess phagicidal activity are Lactococcus lactis phage P001 and Lactococcus lactis phage P008.

Microbial reduction requirements in efficacy testing

Bactericidal efficacy is confirmed when a reduction of ≥5 log is achieved, and this applies to both the preliminary test and the actual test. Confirmation of fungicidal, mycobactericidal, virucidal and phagicidal activity is obtained by achieving log ≥4The exception are the requirements for spores, where in PT2 of the medical area it is necessary to achieve a reduction above 4 logarithms. Whereas in the industrial, domestic and institutional area (PT2 except for the medical area) as well as in the veterinary (PT3) and food area (PT4) this requirement is ≥3 log.

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