Inactivation of SARS-CoV-2 by Simulated Sunlight on Contaminated Surfaces.

We studied the stability of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) under different simulated outdoor conditions by changing the temperature (20°C and 35°C), the illuminance (darkness, 10 klx, and 56 klx), and/or the cleanness of the surfaces at 50% relative humidity (RH). In darkness, the loss of viability of the virus on stainless steel is temperature dependent, but this is hidden by the effect of the sunlight from the first minutes of exposure. The virus shows a sensitivity to sunlight proportional to the illuminance intensity of the sunlight. The presence of interfering substances has a moderate effect on virus viability even with an elevated illuminance. Thus, SARS-CoV-2 is rapidly inactivated by simulated sunlight in the presence or absence of high levels of interfering substances at 20°C or 35°C and 50% relative humidity. IMPORTANCE Clinical matrix contains high levels of interfering substances. This study is the first to reveal that the presence of high levels of interfering substances had little impact on the persistence of SARS-CoV-2 on stainless steel following exposure to simulated sunlight. Thus, SARS-CoV-2 should be rapidly inactivated in outdoor environments in the presence or absence of interfering substances. Our results indicate that transmission of SARS-CoV-2 is unlikely to occur through outdoor surfaces, dependent on illuminance intensity. Moreover, most studies are interested in lineage S of SARS-CoV-2. In our experiments, we studied the stability of L-type strains, which comprise the majority of strains isolated from worldwide patients. Nevertheless, the effect of sunlight seems to be similar regardless of the strain studied, suggesting that the greater spread of certain variants is not correlated with better survival in outdoor conditions.

Active Versus Passive Flow Control in UVC FILTERs for COVID-19 Containment.

Ultraviolet radiation as a germicide is widely used in the health field and even in domestic hygiene. Here, we propose an improvement in low-cost portable units of filtration for indoor air, which is based on ultraviolet radiation. In the current technology, to carry out an air filtration with a suspension of aerosols in which there is a likely concentration of pathogens, whether viral, bacterial or molds, the air is forced to pass as close as possible to the ionizing radiation source (near field). Since the optical mass is very small, the desired effect can be achieved in a considerably short time, deactivating the infective potential of these biological agents. The proposal of this work is the regulation of the flow or speed control of passage through these filters by passive elements instead of by electronic control systems. For this, two devices have been designed, simulated, and built, obtaining similar net pathogen inactivation rates under different flow rates. The passive flow control device has demonstrated higher performance in terms of flow rate and lower cost of production since they do not require electronics and are produced with fewer diodes. This passive device has also shown a lower projection of maintenance cost, lower energy consumption rate (higher efficiency), and longer projection of useful life.

Simulated sunlight decreases the viability of SARS-CoV-2 in mucus.

The novel coronavirus, SARS-CoV-2, has spread into a pandemic since its emergence in Wuhan, China in December of 2019. This has been facilitated by its high transmissibility within the human population and its ability to remain viable on inanimate surfaces for an extended period. To address the latter, we examined the effect of simulated sunlight on the viability of SARS-CoV-2 spiked into tissue culture medium or mucus. The study revealed that inactivation took 37 minutes in medium and 107 minutes in mucus. These times-to-inactivation were unexpected since they are longer than have been observed in other studies. From this work, we demonstrate that sunlight represents an effective decontamination method but the speed of decontamination is variable based on the underlying matrix. This information has an important impact on the development of infection prevention and control protocols to reduce the spread of this deadly pathogen.

Photoinactivation of the Coronavirus Surrogate phi6 by Visible Light.

To stop the coronavirus spread, new inactivation approaches are being sought that can also be applied in the presence of humans or even on humans. Here, we investigate the effect of visible violet light with a wavelength of 405 nm on the coronavirus surrogate phi6 in two aqueous solutions that are free of photosensitizers. A dose of 1300 J cm-2 of 405 nm irradiation reduces the phi6 plaque-forming unit concentration by three log-levels. The next step should be similar visible light photoinactivation investigations on coronaviruses, which cannot be performed in our lab.