Authors: Haymet A, Bassi GL, Fraser JF
PMID: 33170330 PMCID: PMC7652914 DOI: 10.1007/s00134-020-06314-w
Abstract
In 2020, a new pandemic caused by SARS-CoV-2 was declared, and since the first cases of coronavirus disease 2019 (COVID-19), clinicians had to apply different modes of respiratory support, previously used on patients with severe respiratory failure from other etiologies. In particular, high-flow nasal cannulae (HFNC) and non-invasive ventilation (NIV) were variably applied in early reports from China and Europe. Yet, the extent of airborne contamination of clinical areas during the use of HFNC has sparked intense debate and highlighted the need for inclusive investigation in this area.
SARS-CoV-2 may be spread by direct or indirect contact with infected individuals through respiratory secretions or droplet transmission, as well as through fomites. Once airborne, the half-life of SARS-CoV-2 is approximately one hour [95% credible interval, 0.64 to 2.64]. Airborne transmission was initially underestimated; indeed in one analysis in February 2020 of 75,465 cases in China, airborne transmission was not reported. A later study by Liu et al. from Wuhan analyzed aerosol samples using droplet digital polymerase chain reaction, and concluded that virus aerosol deposition on protective apparel or floor surface and their subsequent re-suspension was a conceivable transmission pathway. These findings were further corroborated by Santarpia et al. on 13 isolated patients, who concluded that transmission may occur via contaminated objects and airborne transmission, as well as direct transmission via droplets. Several other factors modulate the specific risk of healthcare workers (HCW) of being infected with SARS-CoV-2 and could be grouped into patient-related and HCW-related risk factors. Patient-related risks are associated with the volume and distance of respiratory particles generated and mobilized from the patient, the viral titre and long-term viability within the aerosolized particles, and finally the ability of the virus to penetrate innate host defenses. In contrast, HCW-related factors are associated to the HCW’s health status, comorbidities and immunocompetency, the length of time of exposure and adequacy of worn personal protective equipment (PPE). Patients with COVID-19 often present to the emergency department with substantial respiratory drive and persistent dry cough. Thus, based on the aforementioned evidence, viral transmission from respiratory particles and droplet dispersion may theoretically pose a significant risk to HCW, specifically in patients who are undergoing means of ventilatory support without shielding their mouths, and during the early days of hospital admission, when the viral load is the highest.
Keywords: SARS-CoV-2, high-flow nasal cannula oxygen therapy, airborne spread
