Study population and setting
Air samples were collected from a single hospital room that housed two COVID-19 patients at the University of Florida Health Shands Hospital. One of the patients had active SARS-CoV-2 infection based on a positive nasopharyngeal test by RT-qPCR. Three, 3-hour air samples of airborne particles were performed serially using two air samplers. The air sampler uses a water-vapor condensation method in order to collect samples. Two samplers were used in order to collect samples from different parts of the room that were placed between 2 and 4.8 meters away from the patients. Material collected in the samples was subjected to RT-qPCR and viral culture; isolated virus extracted from the room and from a nasopharyngeal swab sample were subjected to genome sequencing for comparison.
Summary of Main Findings
Viable virus was isolated from air samples that were collected between 2 and 4.8 meters away (6.5 to 15.7 feet) from the patients. The genome sequence of the isolated virus collected from the air samplers matched that collected from the nasopharyngeal swab. Viral concentrations in the air were estimated to be between 6 and 74 TCID50 (mean tissue culture infectious dose) units/L of air.
While previous studies were unable to isolate the virus, this study utilized a water-vapor condensation mechanism of air sampling, which increases the likelihood of isolating viable virus in tissue culture if virus exists. Further the data came from an area where the patient was known to have SARS-CoV-2 and the viral sequences between the patient and the recovered virus could be compared. Finally, different distances were used to collect the samples to test difference safe distances.
This is a study of a single hospital room and the amount of viable virus isolated per liter of air was small. It is not possible to differentiate whether this small amount of virus was due to the characteristics of the hospital room, infectiousness of the individual infected with SARS-CoV-2, and/or methodological difficulties in actually extracting the virus. It is also not clear how characteristic of the patient affect the amount of detectable virus or the distance at which viral particles can be detected. As these patients were hospitalized, they may have been expressing more viable virus than a patient who was isolating at home.
This study provides evidence that viable SARS-CoV-2 may be found in aerosols, and suggests that further research should be conducted to better understand the role of airborne transmission. It may also point to need to increase recommended distancing protocols if the results are confirmed in other environments and patients.
This review was posted on: 11 September 2020