Validation of the efficacy of air purifiers using molecular techniques.

The importance of air purifiers has increased in recent years, especially with the "coronavirus disease 2019" pandemic. The efficacy of air purifiers is usually determined under laboratory conditions before widespread application. The standard procedure for testing depends on virus cultivation and titration on cell culture. This, however, requires several days to deliver results. The aim of this study was to establish a rapid molecular assay which can differentiate between intact infectious and distorted non-infectious virus particles. Feline Coronavirus was selected as model for screening. First the samples were pretreated with enzymes (universal nuclease and RNase cocktail enzyme mixture) or viability dye (propidium monoazide) to eliminate any free nucleic acids. The ribonucleic acid (RNA) from intact virus was released via magnetic beads-based extraction, then the amount of the RNA was determined using real-time reverse transcription polymerase chain reaction (RT-PCR) or reverse transcription recombinase-aided amplification (RT-RAA). All results were compared to the infectivity assay based on the calculation of the 50% tissue culture infectious dose (TCID50). The nuclease has eliminated 100% of the free Feline Coronavirus RNA, while propidium monoazide underperformed (2.3-fold decrease in free RNA). Both RT-RAA and real-time RT-PCR produced similar results to the infectivity assay on cell culture with limit of detection of 102 TCID50/mL. Two UV-C air purifiers with prosperities of 100% inactivation of the viruses were used to validate the established procedure. Both real-time RT-PCR and RT-RAA were able to differentiate between intact virus particles and free RNA. To conclude, this study revealed a promising rapid method to validate the efficacy of air purifiers by combining enzymatic pretreatment and molecular assays.

The role of toothbrush in the transmission of corona- and influenza viruses - results of an in vitro study.

OBJECTIVES: The aim of this in vitro study was to investigate viruses' stabilities on manual toothbrushes using feline coronavirus (FeCoV) as representative of coronaviruses and an Avian influenza A virus H1N1 for influenza viruses. MATERIAL AND METHODS: Two viruses, FeCoV (Strain Munich; titer 107.5 TCID50/ml) and H1N1 (RE 230/90; titer 106.5 TCID50/ml), were used in this study. Manual toothbrushes were disassembled into bristles, bristle fixation, and back of the toothbrush head, contaminated with the viruses and air-dried for 24 h. In a second experiment, whole toothbrush heads were contaminated, rinsed with water (5 ml for 15 s) and then air-dried. RESULTS: For FeCoV, immediately after contamination, the following average titers were recovered: fixation: 106.41, back of head: 106.81 and bristles: 106.63 TCID50/ml. Following air-drying of 12 (fixation) and 24 h, titers of ≤ 102.5, 103.75, and 102.72 TCID50/ml were found in the respective groups, with a detection limit of 102.5 TCID50/ml. For H1N1, immediately after contamination, the following average titers could be recovered: fixation: 105.53, back of head: 105.97 and bristles: 105.75 TCID50/ml. Following air-drying of 8 (fixation) and 24 h, titers were ≤ 102.5, 103.63, and 103.53 TCID50/ml in the respective group, again with 102.5 TCID50/ml being the detection limit. In case of water rinse, no infectious virus could be recovered after 12 h. CONCLUSION: Viral load of both viruses is reduced by air-drying, especially following water rinsing. Clinical relevance The toothbrush itself plays an insignificant role in the self-transmission of coronavirus and influenza virus.