Characterization of Airborne SARS-CoV-2 in a Veterans Affairs Medical Center

Rationale: The mechanism for spread of Coronavirus Disease 2019 (COVID-19) has been attributed to large droplets produced by coughing and sneezing. There is controversy whether smaller particles may transport Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19. Smaller particles, referred to as fine particulate matter (≤2.5 μm in diameter), can remain airborne for longer periods than larger particles and after inhalation will penetrate deeply into the lungs. Little is known about the size distribution and location of airborne SARS-CoV-2 RNA in a hospital setting. Methods: As a measure of hospitalrelated exposure, air samples of three particle sizes (>10.0 μm, 10.0-2.5 μm, and ≤2.5 μm) were collected at Veterans Affairs Boston Healthcare System from April to May 2020 (N=90 size-fractionated samples) using a custom-built cascade impactor. Locations included outside negative-pressure COVID-19 wards, a hospital ward not directly involved in COVID-19 patient care, and the emergency department. Results: SARS-CoV-2 RNA was present in 9% of samples and in all size fractions at concentrations of 5 to 51 copies m-3. Locations outside COVID-19 wards had the fewest positive samples. A non-COVID-19 ward had the highest number of positive samples, likely reflecting staff congregation. Among all locations, the probability of a positive sample was positively associated (r=0.95, p<0.01) with the number of COVID-19 patients in the hospital, which reflected (r=0.99, p<0.01) the number of new daily cases of COVID-19 in Massachusetts. Conclusions: More frequent detection of positive samples in non-COVID-19 wards than outside COVID-19 hospital areas indicates effectiveness of COVID-ward hospital controls in controlling air concentrations and suggests the potential for disease spread in areas without the strictest precautions. The positive associations noted between the probability of a positive sample, COVID-19 cases in the hospital, and cases in Massachusetts suggests that hospital air sample positivity was related to community burden. The finding of SARS-CoV-2 RNA in samples of fine particulate matter supports the possibility of airborne transmission over distances greater than six feet. The findings support guidelines that limit exposure to airborne particles including fine particles capable of longer distance transport and greater lung penetration.