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New research carried out in collaboration with the University of Birmingham has found that the use of non-invasive breathing support to treat patients with moderate to severe COVID-19 in hospitals isn’t linked to a heightened risk of transmitting infection to others as currently thought.

The use of non-invasive breathing support, called continuous positive airways pressure (CPAP) and high-flow nasal oxygen (HFNO), produced little measurable air or surface viral contamination, and not more than simple oxygen therapy, found the study which was carried out by a team of experts from organisations including the University of Birmingham, Queen’s University Belfast, University Hospitals Birmingham NHS Foundation Trust, and the Universities of Warwick, Liverpool and Edinburgh, and was funded by the National Institute for Health Research (NIHR) and the Medical Research Council.

CPAP delivers a steady level of pressurised air and oxygen through a face mask to assist breathing, while HFNO delivers oxygen at high flow rate through two small tubes in the nose. Both CPAP and HFNO have been thought to be ‘aerosol generating procedures’ which expose healthcare staff and other patients to a heightened infection rate. CPAP and HFNO have been thought to generate particles containing virus capable of contaminating the air and surfaces nearby, necessitating additional infection control precautions such as segregating patients and wearing protective gear to prevent the risk of aerosol transmission.

Researcher Professor Danny McAuley, Professor at Queen’s University Belfast and Consultant in Intensive Care Medicine at the Royal Victoria Hospital, said: “Our findings show that the non-invasive breathing support methods do not pose a higher risk of transmitting infection, which has significant implications for the management of the patients. If there isn’t a higher risk of infection transmission, current practices may be over cautious measures for certain settings, for example preventing relatives visiting the sickest patients, whilst underestimating the risk in other settings, such as coughing patients with early infection on general wards.”

The research involved 30 patients with moderate to severe COVID-19 across three hospitals in the UK. The patients were divided into three groups of 10 and given either supplemental oxygen, CPAP, or HFNO to compare the amount of air and surface environmental contamination with SARS-CoV-2.

Each patient was swabbed for SARS-CoV-2 and had three air and three surface samples collected from the immediate vicinity where healthcare workers provide care. The presence of viral RNA was detected by PCR targeting two viral genes, and positive or suspected-positive samples were then cultured for any demonstration of viable virus.

Dr Christopher Green, Consultant Physician in Infectious Diseases at University Hospitals Birmingham NHS Foundation Trust and Senior Clinical Lecturer at the University of Birmingham, said: “Our study builds on the combined work of ISARIC and the RECOVERY-RS trial, which looked at COVID-19 admissions and the use of non-invasive ventilatory support, or NIV, to treat moderate-to-severe disease. Although more research is needed to confirm our findings, this is the first indication that NIV care such as CPAP or HFNO may not justify their current classification of being 'aerosol-generating' procedures. I’d like to thank everyone involved in this work in Birmingham, with particular thanks to the patients who took part at a very difficult time for each of them, but who were still keen to support research that was focused on understanding the risks to the healthcare workers giving care to them and other patients.”

Overall, 21 (70%) patients tested positive for SARS-CoV-2 by PCR nasopharyngeal swab at the time of assessment. But only 4 out of 90 (4%) air samples were PCR positive.
Neither the use of CPAP nor HFNO nor coughing were associated with significantly more environmental contamination than supplemental oxygen use. Of the total of 51 positive or suspected-positive samples by viral PCR detection, only one sample from the nasopharynx of an HFNO patient was shown as biologically viable in cell culture assay.

The study, published in Thorax, has prompted the researchers to call for a thorough reassessment of the infection control measures deployed for the non-invasive ventilation support methods.

Professor Gavin Perkins of Warwick Clinical Trials Unit at the University of Warwick said: “Infection prevention and control policies are important for protecting patients and NHS workers, but the evidence base relating to aerosol generating procedures is limited. Our research suggests the risks associated with CPAP and HFNO may be less than originally thought and should prompt an evidence based review of infection control practice guidelines.”

Professor McAuley added: “CPAP is being adopted into clinical care pathways for appropriate hospital admissions across all NHS hospitals. It is timely that we can now demonstrate that CPAP doesn’t put others at any higher risk when treating the patient.”

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  • McAuley et al (Nov, 2021). ‘SARS-CoV-2 environmental contamination from hospitalised patients with COVID-19 receiving aerosol-generating procedures’. Thorax. DOI:10.1136/thoraxjnl-2021-218035
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