Disinfection effectiveness test for contaminated surgical mask using an ozone generator | BMC Infectious Diseases

Wearing a mask is one of the best practices to prevent the spread and infection of COVID-19, as recommended by the World Health Organization (WHO). It could also be used for other pandemic infections. Several methods, such as high temperature, UV, ozone, and hydrogen peroxide, have been applied for reuse, disinfection, and sterilization of disposable masks to avoid lack of use in crisis and for safety. Each type of mask may require a different method depending on the material used in construction.

Here we propose the application of O₃ in a container of a certain size for the reduction and elimination of bacteria and viruses on the material of surgical masks. A surgical mask is a tool widely used by medical personnel in hospitals as well as ordinary people. However, studies regarding the reuse, disinfection, and sterilization of surgical masks are sparse compared to those of N95 or filtering facepiece respirators (FFPs). [14].

Our results indicated the efficacy of low dose O₃ (2000 mg/L: 1.02 ppm and 500 mg/L: 0.26 ppm) in the decontamination of surgical masks by reducing the amount and inhibiting the growth of viruses, bacteria and fungi after 15 min, 30 min and 2 h of O treatment₃ produced from modified PZ 2–4, which generates 2000 mg O₃/L in a 0.53 m³ box. The results are similar to the findings of previous studies in terms of the effectiveness of O₃ to kill pathogens on surfaces. Dennis et al. found that gaseous O₃ SARS-CoV-2 inactivated. They also offered a practical recommendation to implement a simple O₃ disinfection box for FFP respirators with 10–20 ppm O₃ for at least 10 min. Literature suggests that ozone attacks capsid proteins in non-enveloped viruses and more easily attacks enveloped viruses [15, 16]. The efficiency of O₃ to kill viruses depends on relative humidity, temperature and type of virus, as shown by Dubuis et al. 2020, who reported that a higher effect of low-dose O₃ exposure (0.23–1.23 ppm) for norovirus inactivation was found at 85% relative humidity (RH) for 40 min of norovirus, while 20% relative humidity for 10 min gave the same result for bacteriophages. These results suggest that high RH should be used with O₃ to obtain a powerful disinfectant of airborne viruses, which could be implemented inside naturally ventilated hospital rooms. However, this study was carried out under temperature and humidity conditions in August in Thailand without measuring the exact temperature and relative humidity, although the average temperature was 28 ° C and the average relative humidity was 83 .2% according to the August 2020 agrometeorological report of the meteorological service [17].

Gram-negative bacteria and fungi require more time for decontamination. There are many reports of O₃ reduce the number of bacteria, viruses, and bacterial spores on the surface of materials, including figs, fabrics, and plastics, to a relatively low concentration of 1-25 ppm in an average time of 1-4 hours [18, 19]. These results are related to this study and to the experience of P. aeruginosa and S. aureus closed system disinfection in a closed system, which showed that bacteria at a concentration of 10³ CFU/mL were eliminated in 30 min and chamber sterilization was achieved in 4 h. In addition, this experiment succeeded in the fungal inactivation of Aspergillus spp. by ozone in a closed system ozone incubator within 120 min. This may be related to previous studies that showed similar results for fungal inactivation. Wood et al. reported on the inactivation of spores of Bacillus anthracis and Bacillus subtilis on building materials by O₃ [20]. O₃ can diffuse through the cell membrane, and the attack of glycoproteins and glycolipids in the cell membrane leads to the rupture of pathogenic cells. Moreover, O₃ attacks the sulfhydryl groups of certain enzymes, leading to disruption of normal cellular enzyme activity and loss of function. Ozone also attacks the purine and pyrimidine bases of nucleic acids, damaging DNA [21, 22]. The advantages of ozone gas are that it reaches shadows and crevices during the disinfection process, unlike ultraviolet radiation which has a short half-life in an air-circulating environment. The concentration immediately dangerous to life or health (IDLH) of ozone is 5 ppm for humans. Exposure to 50 ppm for 60 min will likely be fatal to humans [23]. Therefore, a low dose in a closed system should be used to avoid direct contact. However, O₃ gas can be exchanged quickly by O_2, and the smell of O₃ is detectable by many people at low concentrations of 0.1 ppm in air in a domestic environment with air changes per hour varying between 5 and 8 ACH. Ozone has a half-life as short as 30 min [24], and the reaction proceeds faster at higher temperatures (Earth Science FAQ in the image). Our experiment used a generator machine that produced 2000 mg/L in a 0.53 m space³ box.

This study also supported previous studies showing that ozone treatment causes very little degradation of fibrous structures or the fit of surgical masks. Unlike other decontamination procedures, such as UV treatment, which allows re-use a limited number of times due to negative side effects including elastic deformation, moisture build-up and destruction of the fibrous material. This suggested that O₃ the treatment could maintain the filtration capacity of a mask for reuse more than 30 times [25].

Only 2 container sizes and 2 concentrations of O₃ were used in this study. The temperature and humidity during the experiment were not fixed, which may affect the disinfecting effectiveness of ozone, and the filtration capacity of the surgical mask was not determined.