Discussion

Air samples near patients under NIRS were infrequently positive for SARS-CoV-2 (10%), and none of these RT-PCR-positive samples was positive in viral culture. Our findings indicate that COVID-19 patients might use NIRS and that concerns regarding aerosolization should probably not be a reason to withhold NIRS strategies.

NIRS have been put under the umbrella of aerosol-generating procedures,^{Reference Klompas, Baker and Rhee5} though there is controversy. SARS-CoV-2 spreads when symptomatic or asymptomatic people talk or breathe as much as when they cough. A struggling patient with overt dyspnea and cough probably generates many particles to ambient air, whereas NIRS does not necessarily increase aerosol generation. If dyspnea is adequately controlled and the patient stays comfortable with either NIPPV or HFNO, then aerosol generation is probably not an important issue. Exhaled aerosols occur in multiple sizes that are associated with different generation sites and production mechanisms in the respiratory tract.^{Reference Wang, Prather, Sznitman, Jimenez, Lakdawala, Tufekci and Marr6} In healthy individuals, neither HFNO nor NIPPV increase the risk of aerosolization when measured by an aerodynamic particle spectrometer.^{Reference Gaeckle, Lee, Park, Kreykes, Evans and Hogan7}

We compared PCR positivity for NIPPV, HFNO, and the ICU aisle. A recent study reported 30% positivity among 40 air samples, without detection of viable virus.^{Reference Lebreil, Vincent and Glenet8} They also reported that air contamination was no different from patients under invasive mechanical ventilation and HFNO, suggesting that the ventilatory strategy does not increase aerosol generation. Another study assessed whether HFNO or continuous positive airway pressure was associated with increased levels of viral RNA in air samples compared to standard oxygen therapy.^{Reference Winslow, Zhou and Windle9} Only 30% participants had at least 1 positive or suspected positive result and they showed that Ct values were much higher than a paired nasopharyngeal sample. Also, they did not observe viable culturable virus in their PCR positive samples.

Our study had several limitations. We did not prospectively collect Ct values from patients; however, positivity using our method was a Ct value <32, always lower than the corresponding positive air samples. Second, we did not sample surfaces as another surrogate of environmental spread, although fomites are likely not the main transmission route. Third, air samples were collected mainly from patients in the second week of disease and may have been less infective; nevertheless, this timing is representative of patients with the timing of respiratory failure onset and potential need for NIRS.

In our study, neither NIPPV nor HFNO appeared to have been associated with a higher risk of aerosol generation than being at the bedside of patients with COVID-19.