Validated computational modelling to evaluate spatial inactivation of airborne pathogens by Far-UVC irradiation.

Recent experimental studies have indicated the potential for ultraviolet-C irradiation at 222nm (Far-UVC) to be used in occupied rooms to safely reduce exposure to airborne pathogens. We present simulations applying a Monte Carlo radiation transfer model with a computational fluid dynamics model to predict the spatial variation in airborne microorganism inactivation. Our simulations effectively reproduce data from steady state experiments in a room-sized bio-aerosol chamber for the reduction of aerosolised Staphylococcus aureus. Application of the validated model suggests that germicidal Far-UVC lamps could reduce levels of airborne human coronavirus by more than 90% in rooms with low ventilation rates. The inactivation of pathogens by Far-UVC is more efficient than previously thought, due to the complex path that particles take within the three dimensional airflow and UVC irradiance pattern. Depending on the UVC-susceptibility of the aerosolised pathogen, Far-UVC lamps have the potential to provide effective room air change rates in excess of 100 equivalent air changes per hour, much greater than is possible with mechanical ventilation or filtration devices. The success of our simulations at reproducing the experimental data provides confidence that we can simulate larger environments and inform best practices for installations of germicidal Far-UVC lamps.

Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber.

Many infectious diseases, including COVID-19, are transmitted by airborne pathogens. There is a need for effective environmental control measures which, ideally, are not reliant on human behaviour. One potential solution is Krypton Chloride (KrCl) excimer lamps (often referred to as Far-UVC), which can efficiently inactivate pathogens, such as coronaviruses and influenza, in air. Research demonstrates that when KrCl lamps are filtered to remove longer-wavelength ultraviolet emissions they do not induce acute reactions in the skin or eyes, nor delayed effects such as skin cancer. While there is laboratory evidence for Far-UVC efficacy, there is limited evidence in full-sized rooms. For the first time, we show that Far-UVC deployed in a room-sized chamber effectively inactivates aerosolised Staphylococcus aureus. At a room ventilation rate of 3 air-changes-per-hour (ACH), with 5 filtered-sources the steady-state pathogen load was reduced by 98.4% providing an additional 184 equivalent air changes (eACH). This reduction was achieved using Far-UVC irradiances consistent with current American Conference of Governmental Industrial Hygienists threshold limit values for skin for a continuous 8-h exposure. Our data indicate that Far-UVC is likely to be more effective against common airborne viruses, including SARS-CoV-2, than bacteria and should thus be an effective and "hands-off" technology to reduce airborne disease transmission. The findings provide room-scale data to support the design and development of effective Far-UVC systems.

Association Between COVID-19 Diagnosis and In-Hospital Mortality in Patients Hospitalized With ST-Segment Elevation Myocardial Infarction.

IMPORTANCE: There has been limited research on patients with ST-segment elevation myocardial infarction (STEMI) and COVID-19. OBJECTIVE: To compare characteristics, treatment, and outcomes of patients with STEMI with vs without COVID-19 infection. DESIGN, SETTING, AND PARTICIPANTS: Retrospective cohort study of consecutive adult patients admitted between January 2019 and December 2020 (end of follow-up in January 2021) with out-of-hospital or in-hospital STEMI at 509 US centers in the Vizient Clinical Database (N = 80 449). EXPOSURES: Active COVID-19 infection present during the same encounter. MAIN OUTCOMES AND MEASURES: The primary outcome was in-hospital mortality. Patients were propensity matched on the likelihood of COVID-19 diagnosis. In the main analysis, patients with COVID-19 were compared with those without COVID-19 during the previous calendar year. RESULTS: The out-of-hospital STEMI group included 76 434 patients (551 with COVID-19 vs 2755 without COVID-19 after matching) from 370 centers (64.1% aged 51-74 years; 70.3% men). The in-hospital STEMI group included 4015 patients (252 with COVID-19 vs 756 without COVID-19 after matching) from 353 centers (58.3% aged 51-74 years; 60.7% men). In patients with out-of-hospital STEMI, there was no significant difference in the likelihood of undergoing primary percutaneous coronary intervention by COVID-19 status; patients with in-hospital STEMI and COVID-19 were significantly less likely to undergo invasive diagnostic or therapeutic coronary procedures than those without COVID-19. Among patients with out-of-hospital STEMI and COVID-19 vs out-of-hospital STEMI without COVID-19, the rates of in-hospital mortality were 15.2% vs 11.2% (absolute difference, 4.1% [95% CI, 1.1%-7.0%]; P = .007). Among patients with in-hospital STEMI and COVID-19 vs in-hospital STEMI without COVID-19, the rates of in-hospital mortality were 78.5% vs 46.1% (absolute difference, 32.4% [95% CI, 29.0%-35.9%]; P < .001). CONCLUSIONS AND RELEVANCE: Among patients with out-of-hospital or in-hospital STEMI, a concomitant diagnosis of COVID-19 was significantly associated with higher rates of in-hospital mortality compared with patients without a diagnosis of COVID-19 from the past year. Further research is required to understand the potential mechanisms underlying this association.

Turn Up the Lights, Leave them On and Shine them All Around-Numerical Simulations Point the Way to more Efficient Use of Far-UVC Lights for the Inactivation of Airborne Coronavirus.

It has been demonstrated in laboratory environments that ultraviolet-C (UVC) light is effective at inactivating airborne viruses. However, due to multiple parameters, it cannot be assumed that the air inside a room will be efficiently disinfected by commercial germicidal ultraviolet (GUV) systems. This research utilizes numerical simulations of airflow, viral spread, inactivation by UVC and removal by mechanical ventilation in a typical classroom. The viral load in the classroom is compared for conventional upper-room GUV and the emerging "Far-UVC." In our simulated environment, GUV is shown to be effective in both well and poorly ventilated rooms, with greatest benefit in the latter. At current exposure limits, 18 commercial Far-UVC systems were as effective at reducing viral load as a single upper-room GUV. Improvements in Far-UVC irradiation distribution and recently proposed increases to exposure limits would dramatically increase the efficacy of Far-UVC devices. Modifications to current Far-UVC devices, which would improve their real-world efficacy, could be implemented now without requiring legislative change. The prospect of increased safety limits coupled with our suggested technological modifications could usher in a new era of safe and rapid whole room air disinfection in occupied indoor spaces.

Extreme Exposure to Filtered Far-UVC: A Case Study†.

Far-UVC devices are being commercially sold as "safe for humans" for the inactivation of SARS-CoV-2, without supporting human safety data. We felt there was a need for rapid proof-of-concept human self-exposure, to inform future controlled research and promote informed discussion. A Fitzpatrick Skin Type II individual exposed their inner forearms to large radiant exposures from a filtered Krypton-Chloride (KrCl) far-UVC system (SafeZoneUVC, Ushio Inc., Tokyo, Japan) with peak emission at 222 nm. No visible skin changes were observed at 1500 mJ cm-2 ; whereas, skin yellowing that appeared immediately and resolved within 24 h occurred with a 6000 mJ cm-2 exposure. No erythema was observed at any time point with exposures up to 18 000 mJ cm-2 . These results combined with Monte Carlo Radiative Transfer computer modeling suggest that filtering longer ultraviolet wavelengths is critical for the human skin safety of far-UVC devices. This work also contributes to growing arguments for the exploration of exposure limit expansion, which would subsequently enable faster inactivation of viruses.