Tuesday, July 21, 2020

Study: The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol


Photo Credit PHIL


#15,373

For nearly six months we've been watching the scientific debate over whether SARS-CoV-2 can be spread via patient-generated aerosols (aka `is airborne').  

This makes a huge difference - particularly for healthcare workers - because it dictates the level of PPEs that HCWs should be wearing when in close contact with a patient. 

We've followed the research, and the debate closely for months, including:

Scientists `Airborne' Letter To WHO & Another SARS-CoV-2 Ventilation Dispersal Study

EID Journal: Persistence of SARS-CoV-2 in Aerosol Suspensions
 

Despite limited evidence, the CDC decided early on to err on the side of caution, and back in February, advised:
Ask such patients to wear a face mask as soon as they are identified. Conduct patient evaluation in a private room with the door closed, ideally an airborne infection isolation room, if available. Personnel entering the room should use standard precautions, contact precautions, and airborne precautions, and use eye protection (goggles or a face shield). 
Recently, they upped the ante even more, warning:
Below are changes to the guidance as of July 15, 2020:
  • Added language that protective eyewear (e.g., safety glasses, trauma glasses) with gaps between glasses and the face likely do not protect eyes from all splashes and sprays.
Meanwhile many other public health agencies and organizations - including the World Health Organization - continue to issue less stringent `Droplet' guidance, pointing out that while there have been studies suggestive of `airborne' transmission, overall the evidence for that has been weak. 

And to be fair, many of these past studies have used artificial aerosolization techniques - not direct real time measurements from patients - and while RT-PCR testing has shown evidence of SARS-CoV-2 genetic material in aerosols and on fomites some distance from patients, the virus had not been proven to remain infectious. 

Today we've a new study, from researchers at the University of Nebraska Medical Center, that addresses both of these shortcomings. While not currently a peer-reviewed paper, UNMC is well versed in dealing with airborne viruses, being one of a handful of National Ebola Training and Education Centers in the country.

Not only were these researchers able capture aerosolized virus particles in patient's room air, they were able to demonstrate viability, by growing them in cell cultures.
 
I've only posted the abstract and the author's conclusions.  Follow the link to read the study in its entirety.
The Infectious Nature of Patient-Generated SARS-CoV-2 Aerosol
Joshua L Santarpia, Vicki L Herrera, Danielle N Rivera, Shanna Ratnesar-Shumate, St. Patrick Reid, Paul W Denton, Jacob W.S. Martens, Ying Fang, Nicholas Conoan, Michael V Callahan, James V Lawler, David M Brett-Major, John J Lowe
doi: https://doi.org/10.1101/2020.07.13.20041632

This article is a preprint and has not been certified by peer review 
 

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission causing coronavirus disease 2019 (COVID-19) may occur through multiple routes.
We collected aerosol samples around six patients admitted into mixed acuity wards in April of 2020 to identify the risk of airborne SARS-CoV-2. Measurements were made to characterize the size distribution of aerosol particles, and size-fractionated, aerosol samples were collected to assess the presence of infectious virus in particles sizes of >4.1 μm, 1-4 μm, and <1 μm in the patient environment. Samples were analyzed by real-time reverse-transcriptase polymerase chain reaction (rRT-PCR), cell culture, western blot, and transmission electron microscopy (TEM).
SARS-CoV-2 RNA was detected in all six rooms in all particle size fractions (>4.1 μm, 1-4 μm, and <1 μm). Increases in viral RNA during cell culture of the virus from recovered aerosol samples demonstrated the presence of infectious, replicating virions in three <1 μm aerosol samples (P<0.05). Viral replication of aerosol was also observed in the 1-4 μm stage but did not reach statistical significance (0.05<P<0.10). Western blot and TEM analysis of these samples also showed evidence of viral proteins and intact virions.
The infectious nature of aerosol collected in this study further suggests that airborne transmission of COVID-19 is possible, and that aerosol prevention measures are necessary to effectively stem the spread of SARS-CoV-2.
        (SNIP)
Conclusion

 Our results demonstrate that SARS-CoV-2 RNA exists in respired aerosols less than 5 µm in diameter; that aerosols containing SARS-CoV-2 RNA exist in particle modes that are produced during respiration, vocalization, and coughing; and that some fraction of the RNA-containing aerosols contain infectious virions (Table S7).
This study supports the use of efficient respiratory protection and airborne isolation precautions to protect from exposure to fine SARS-CoV-2 aerosol when interacting with infected individuals, regardless of symptoms or medical procedure being performed. Given the prospect of continued widespread circulation of COVID-19, and recent work highlighting the relative importance of airborne transmission of COVID-195 , it is crucial that evidenced-based IPC practices are promoted and implemented to limit the transmission of SARS-CoV-2 in healthcare, community and industry settings.
Given the infectious nature of aerosol collected in this study, taken with the other lines of evidence presented, further suggests that airborne transmission of COVID-19 is possible, and that aerosol prevention measures should be implemented to effectively stem the spread of SARS-CoV-2, particularly in crowded settings.

All of this has implications, not only for Health Care Workers and their PPEs, but for the rest of us as well.

It supports that notion that crowded indoor venues represent a higher risk environment, raises additional questions over the potential spread of the virus by ventilation systems, and suggests that the 2-meter separation rule may not always be adequate.

It also reinforces the idea that universal masking to prevent the spread of the virus is crucial.  While less than ideal for preventing someone from catching the virus, it can significantly reduce the amount of aerosolized virus being expelled by those who are infected. 

Although there remain many other questions, and this is unlikely to be the last word on the subject - given what we know now - it would be a terrible mistake to continue to underestimate the transmissibility of this virus.  
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