Expiratory Aerosol pH: The Overlooked Driver of Airborne Virus Inactivation.

Respiratory viruses, including influenza virus and SARS-CoV-2, are transmitted by the airborne route. Air filtration and ventilation mechanically reduce the concentration of airborne viruses and are necessary tools for disease mitigation. However, they ignore the potential impact of the chemical environment surrounding aerosolized viruses, which determines the aerosol pH. Atmospheric aerosol gravitates toward acidic pH, and enveloped viruses are prone to inactivation at strong acidity levels. Yet, the acidity of expiratory aerosol particles and its effect on airborne virus persistence have not been examined. Here, we combine pH-dependent inactivation rates of influenza A virus (IAV) and SARS-CoV-2 with microphysical properties of respiratory fluids using a biophysical aerosol model. We find that particles exhaled into indoor air (with relative humidity ≥ 50%) become mildly acidic (pH ∼ 4), rapidly inactivating IAV within minutes, whereas SARS-CoV-2 requires days. If indoor air is enriched with nonhazardous levels of nitric acid, aerosol pH drops by up to 2 units, decreasing 99%-inactivation times for both viruses in small aerosol particles to below 30 s. Conversely, unintentional removal of volatile acids from indoor air may elevate pH and prolong airborne virus persistence. The overlooked role of aerosol acidity has profound implications for virus transmission and mitigation strategies.

‘I left feeling different about myself’: What students learn on their first practice placement

Introduction: With the inclusion of 40 hours of simulated practice education for UK occupational therapy students and the subsequent impact of the COVID-19 pandemic, universities have been exploring simulated placement opportunities. However, the evidence available to guide the development of such placements is sparse. This article presents the first stage of a grounded theory study that seeks to understand what students learn during the course of their first practice placement, with the intention of informing simulated placement development. Method: Grounded theory methodology was used to guide semi-structured individual interviews with 15 participants - seven undergraduate students, three practice educators and five postgraduate pre-registration students. Interviews occurred close to the end of the first practice placement. Concurrent data collection and analysis led to the development of categories of learning. Findings: Four core categories of learning were identified: learning about oneself, learning about the occupational therapy profession, learning about practices and learning about service users. Conclusion: Understanding of these four categories of learning may enable educators to consider learning which occurs that may not be anticipated, particularly in regard to personal development. This can enable educators to consider how learning can be targeted within simulation for an authentic simulated placement.

Change in stroke presentations during COVID-19 pandemic in South-Western Sydney. (preprint)

Background: Australia managed relatively well during the global COVID-19 pandemic owing to our swift mandated public health response. During the NSW lockdown restrictions, we noted a decrease in acute stroke presentations at our institution, similar to what was subsequently reported worldwide. Aims: We aimed to test our hypothesis that (i) the true numbers of ischaemic strokes did not change, however patients were presenting later and (ii) the proportion of TIAs decreased. Methods: We conducted a retrospective audit of all stroke and TIA presentations in 2020 and compared these with data from 2019. We collected information about stroke subtype, severity, time from stroke/TIA onset to presentation and acute reperfusion therapies. Results: Between January-February and April-March 2020, there was a 15% drop in acute stroke presentations (128 vs. 109). In the same period "stroke mimic" presentations dropped by 22%. The proportion of patients attending the emergency department within 4.5hrs was only 36% compared with 48% over the similar period in 2019. Conclusions: Although the raw numbers of ischemic stroke presentations remained stable during NSW Covid lockdown, the proportion of patients presenting within time window for acute reperfusion therapies fell. The number of TIAs similarly fell suggesting COVID-19 discouraged patients from presenting to hospital which placed them at higher risk of disabling stroke. The opportunity cost of lockdown restrictions on stroke outcome should be considered in future policy directives.

The impact of Spike mutations on SARS-CoV-2 neutralization (preprint)

Multiple SARS-CoV-2 vaccines have shown protective efficacy, which is most likely mediated by neutralizing antibodies recognizing the viral entry protein, Spike. Antibodies from SARS-CoV-2 infection neutralize the virus by focused targeting of Spike and there is limited serum cross-neutralization of the closely-related SARS-CoV. As new SARS-CoV-2 variants are rapidly emerging, exemplified by the B.1.1.7, 501Y.V2 and P.1 lineages, it is critical to understand if antibody responses induced by infection with the original SARS-CoV-2 virus or the current vaccines will remain effective against virus variants. In this study we evaluate neutralization of a series of mutated Spike pseudotypes including a B.1.1.7 Spike pseudotype. The analyses of a panel of Spike-specific monoclonal antibodies revealed that the neutralizing activity of some antibodies was dramatically reduced by Spike mutations. In contrast, polyclonal antibodies in the serum of patients infected in early 2020 remained active against most mutated Spike pseudotypes. The majority of serum samples were equally able to neutralize the B.1.1.7 Spike pseudotype, however potency was reduced in a small number of samples (3 of 36) by 5-10-fold. This work highlights that changes in the SARS-CoV-2 Spike can alter neutralization sensitivity and underlines the need for effective real-time monitoring of emerging mutations and their impact on vaccine efficacy.

Air recirculation role in the infection with COVID-19, lessons learned from Diamond Princess cruise ship (preprint)

Objectives: The Diamond Princess cruise ship is a unique case because it is the place at which testing capacity has reached its highest rate in the world during the COVID-19 pandemic. By analysing data that are collected about the current COVID-19 outbreak onboard, and by considering the design of the air conditioning system of the ship and virus transmission modes on cruise ships, this study aims to raise the hypothesis regarding the role of poor ventilation systems in the spread of COVID-19. Design: This is an analysis of count data that has been collected by the onboard clinic up to the 20th February 2020. Symptomatic infection rates during the quarantine period in cabins with previous confirmed cases are compared to these in cabins without previous confirmed cases. Results: Symptomatic infection rate during the quarantine period in cabins with previously confirmed cases is not significantly higher than that in cabins without previously confirmed cases. Age does not appear to be a cofounder. Conclusions: Airborne transmission of COVID-19 through the ventilation system onboard could explain the virus spread into cabins during the quarantine period.