From the Journals

New transmission information should motivate hospitals to reexamine aerosol procedures, researchers say



Two studies published in Thorax have found that the use of continuous positive airways pressure (CPAP) or high-flow nasal oxygen (HFNO) to treat moderate to severe COVID-19 is not linked to a heightened risk of infection, as currently thought. Researchers say hospitals should use this information to re-examine aerosol procedures in regard to risk of transmission of SARS-CoV-2.

CPAP and HFNO have been thought to generate virus particles capable of contaminating the air and surfaces, necessitating additional infection control precautions such as segregating patients. However, this research demonstrates that both methods produced little measurable air or surface viral contamination. The amount of contamination was no more than with the use of supplemental oxygen and less than that produced when breathing, speaking, or coughing.

In one study, led by a team from the North Bristol NHS Trust, 25 healthy volunteers and eight hospitalized patients with COVID-19 were recruited and asked to breathe, speak, and cough in ultra-clean, laminar flow theaters followed by use of CPAP and HFNO. Aerosol emission was measured via two methodologies, simultaneously. Hospitalized patients with COVID-19 had cough recorded via the same methodology on the infectious diseases ward.

CPAP (with exhalation port filter) was found to produce less aerosol than breathing, speaking, and coughing, even with large > 50 L/min face mask leaks. Coughing was associated with the highest aerosol emissions of any recorded activity.

HFNO was associated with aerosol emission from the machine. Generated particles were small (< 1 mcm), passing from the machine through the patient and to the detector without coalescence with respiratory aerosol, and, consequently, would be unlikely to carry viral particles.

More aerosol was generated in cough from patients with COVID-19 (n = 8) than from volunteers.

In the second study, 30 hospitalized patients with COVID-19 requiring supplemental oxygen were prospectively enrolled. In this observational environmental sampling study, participants received either supplemental oxygen, CPAP, or HFNO (n = 10 in each group). A nasopharyngeal swab, three air, and three surface samples were collected from each participant and the clinical environment.

Overall, 21 of the 30 participants tested positive for SARS-CoV-2 RNA in the nasopharynx. In contrast, 4 out of 90 air samples and 6 of 90 surface samples tested positive for viral RNA, although there were an additional 10 suspected-positive samples in both air and surfaces samples.

Neither the use of CPAP nor HFNO nor coughing were associated with significantly more environmental contamination than supplemental oxygen use. Of the total positive or suspected-positive samples by viral PCR detection, only one nasopharynx sample from an HFNO patient was biologically viable in cell culture assay.

“Our findings show that the noninvasive breathing support methods do not pose a higher risk of transmitting infection, which has significant implications for the management of the patients,” said coauthor Danny McAuley, MD.

“If there isn’t a higher risk of infection transmission, current practices may be overcautious 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.”

Although both studies are small, the results do suggest that there is a need for an evidence-based reassessment of infection prevention and control measures for noninvasive respiratory support treatments that are currently considered aerosol generating procedures.

A version of this article first appeared on

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