Why does this study matter?
Early studies told us that the SARS-CoV-2 virus was passed from person to person by respiratory droplets. This isn’t unexpected for a respiratory disease at all, but then the next question (that has been an ongoing source of debate) is aerosolization and differentiating droplets from aerosols. Up until the first week of October, the World Health Organization took the position that airborne transmission is only a risk during aerosol generating procedures, like intubation. But many others argued the virus was more generally spread by airborne transmission. This study was a preprint issued in early August and it made the news with headlines in the NY Times the following week as “the smoking gun.” Previous studies on airborne transmission of SARS-CoV-2 used indirect sampling methods that may have detected inactivated virus. But inactive viruses are in the air we breathe all day, every day. These don’t lead to disease. This was the first study to use new direct sampling techniques.
How was the study done?
The researchers, based in a Florida hospital, sampled air for the virus with two types of samplers. The samples were taken in a two-bed patient room occupied by COVID+ patients; Patient 1 was just admitted, Patient 2 was ready for discharge. The room had 6 aire changes per hour (ACH) and included MERV 14 filters, coil condensation, and UV-C irradiation prior to recirculation. The water-vapor condensation mechanism samplers were at opposite ends of the room and located more than 15’ away from the patients. Air samples were collected and isolated in cell culture, and genetically sequenced. Nasal swabs from each patient were also sampled. There were no health-care aerosol-generating procedures performed in the room.
So what do we learn from the study?
Air samples were used with and without HEPA filters. SARS-CoV-2 genomic RNA was detected in material collected from air samples collected without a HEPA filter covering the inlet tube. No SARS-CoV-2 genomes were detected in air samples with the HEPA filter. Since the distance from the air-samplers to the patients was more than 6’, the implication is that the virus was present in the air as an aerosol particle. Infectivity was established by the 50% endpoint dilution assay (TCID50).
A nearly complete SARS-CoV-2 genome sequence was obtained by from cell culture medium of the swab material from patient 1. A complete sequence of SARS-CoV-2 collected from an air sample was compared with three partial sequences from the other air samples and the results indicated the same genome sequence present in all of the other air samples. They were an exact match with the virus isolated from patient 1.
Can we say the results are definitive?
The authors cite one distinct limitation. Plaque assays, which are the standard for evaluating virus viability, were not used due to availability if supplies at the time. But there’s a lot of technical information in this paper. Someone with expertise on viral cell lines, cultured cells, genomic sequencing, and the mechanics of air sampling equipment might have something to more to say, especially because the sampling technique is new. There has been so much back and forth on this topic, it’s really hard to say what’s definitive, but the authors make good points about how they have advanced the limitations of earlier studies, including some of their own. From the author’s perspective, the amount of airborne virus detected per liter of air was small. For them, this raised some questions for future studies. Is this typical for this virus? Is this relative to where the patient is in their phase of the disease? Was this related to air changes in the room? Or particle size? We have some answers, but still many unanswered questions.
What’s the takeaway?
In evidence-based design we talk a lot about the best available credible research at the time. We hope our knowledge is always evolving from the research, and the advent of COVID gave us a huge volume of open-access research – in fact, it’s been called a publishing pandemic. But the vast amounts of information, a lot of it pre-print, and therefore without peer review, brought a level of confusion through conflicting studies that made it pretty difficult for mere mortals to know what to do. For designers, aerosolization raises questions about HVAC systems and air changes, but there are other questions that have been raised about temperature, and relative humidity in other studies, too. But HVAC design wasn’t the purpose of this study, and even though we know there are implications from these results, we all need continued discussions with professional, who can help translate that best available evidence. ASHRAE has been trying to develop guidance in this area, but, this study does clearly suggest there is an inhalation risk for acquiring COVID-19 beyond the 6’ practice of physical or social distancing. In fact, the authors suggest we may actually have a false sense of security that we are protecting ourselves from one another. We should take care, think a little more about the implications for HVAC, and see how the evidence continues to evolve.
Lednicky, J. A., Lauzardo, M., Hugh Fan, Z., Jutla, A., Tilly, T. B., Gangwar, M., Usmani, M., Shankar, S. N., Mohamed, K., Eiguren-Fernandez, A., Stephenson, C. J., Alam, M. M., Elbadry, M. A., Loeb, J. C., Subramaniam, K., Waltzek, T. B., Cherabuddi, K., Glenn Morris, J., & Wu, C. Y. (2020). Viable SARS-CoV-2 in the air of a hospital room with COVID-19 patients. International Journal of Infectious Diseases, 100, 476–482. https://doi.org/10.1016/j.ijid.2020.09.025
Our slidecasts are an outcome of the popular Research Matters presentations at the annual Healthcare Design Expo & Conference. Our research team picks papers that have some significance to the healthcare design community and distill the study down into a 5-minute summary of how the study was done, what was learned, the limitations and the takeaway. The slidecasts bring research to you in digestible format. Just five minutes, and you’ll know more.
