Study of SARS-CoV-2 Finds Airborne Particles, but Are They Infective?
A pre-published study under peer review suggests particles of SARS-CoV-2 can linger on surfaces and travel in the air beyond six feet. Ongoing work is bolstering the initial findings, says Joshua Santarpia, PhD, an associate professor of pathology and microbiology at the University of Nebraska Medical Center.
“Clearly, there is no proof of airborne transmission yet. But we feel like with this and several other studies, there is enough information to suggest that for healthcare workers, airborne isolation is warranted,” he says. “There has been a lot of discussion about ‘We don’t know enough to say whether this is airborne or not.’ I think there is a lot of evidence that suggests it could be. That to me is enough to tell a healthcare worker to protect yourself as much as you can.”
Santarpia and colleagues studied the environment of 13 patients confirmed with COVID-19 infection, collecting air and surface samples in isolation rooms to examine viral shedding.
“While all individuals were confirmed positive for SARS-CoV-2, symptoms and viral shedding to the environment varied considerably,” the authors noted. “Many commonly used items, toilet facilities, and air samples had evidence of viral contamination, indicating that SARS-CoV-2 is shed to the environment as expired particles, during toileting, and through contact with fomites. ”1 Santarpia and colleagues added that disease spread is indicated through both direct contact (droplet and person-to-person) and indirect contact (contaminated objects and airborne transmission), supporting the use of airborne isolation precautions.
Controversial Findings
Although still subject to peer review, the findings are controversial because public health officials originally recommended N95 respirators for healthcare workers treating COVID-19 patients under airborne precautions. The recommendation was temporarily amended to wearing surgical masks if N95s were not available, a stopgap measure that could be reversed as soon as supplies were in stock. That wording appears to have been dropped from current CDC recommendations, which present a variety of options to preserve PPE and reuse N95s if warranted.2
The patients were admitted to the Nebraska Biocontainment Unit (NBU) for individuals requiring hospital care, and the National Quarantine Unit (NQU) for isolation of asymptomatic or mildly ill individuals not requiring hospital care. The patients had private rooms with a bathroom. Healthcare workers wore full personal protective equipment (PPE) with N95 respirators in accordance with airborne precautions. Samples were obtained at various times during hospitalization. The researchers took surface and air samples.
Of the 163 samples collected in the study, 77% had a positive polymerase chain reaction (PCR) result for SARS-CoV-2. Overall, 77% of all personal items sampled were determined to be positive for SARS-CoV-2 by PCR. Eighty-three percent of cellphones tested positive, as did 65% of in-room TV remotes. Room toilets were 81% positive, as were 75% of the bedside tables and bed rails and 82% of the window ledges. Sixty-three percent of in-room air samples were positive, as were 67% of hallway air samples, the researchers reported.
“Air samples that were positive for viral RNA by reverse transcription PCR were examined for viral propagation in Vero E6 cells,” the authors concluded. “Cytopathic effect was not observed in any sample, to date, and immunofluorescence and western blot analysis have not, so far, indicated the presence of viral antigens suggesting viral replication. However, the low concentrations of virus recovered from these samples makes finding infectious virus in these samples difficult. Further experiments are ongoing to determine viral activity in these samples.” Those experiments are showing more signs of viral replication, which should eventually bolster the equivocal findings in the pre-published paper, Santarpia says.
“I believe we had some pretty solid evidence that we were seeing replication in cell culture from one of the surface samples in this study,” he explains. “That is complicated by peer review. There is disagreement whether we demonstrated that or not. In the studies we have done since, we are seeing replication in some fraction of samples we are taking. I would say it is certainly possible; it is not yet proven.”
Finding particles beyond the six-foot social distancing parameter was not that surprising, but the question again is whether they would be infectious. There have been studies since “that indicate the even larger droplets are going to go farther than six feet, which sort of makes sense intuitively,” Santarpia says. “We are working to determine particle size right now, but it does jibe with everything people are working on. [Six feet] is completely arbitrary. The particle size distribution is pretty broad, depending on what [people] are doing.”
For example, some particles in hallways could have been caused by air flow changes as healthcare workers exited the rooms. No healthcare workers were infected, underscoring that wearing full PPE under airborne precautions protects workers from occupational transmission of the coronavirus.
“Taken together, these data indicate significant environmental contamination in rooms where patients infected with SARS-CoV-2 are housed and cared for, regardless of the degree of symptoms or acuity of illness,” the authors concluded. “Contamination exists in all types of samples: high- and low-volume air samples, as well as surface samples, including personal items, room surfaces, and toilets.”
REFERENCES
- Santarpia, JL, Rivera DN, Herrera V, et al. Transmission potential of SARS-CoV-2 in viral shedding observed at the University of Nebraska Medical Center. Preprint article under peer review. 2020;doi: https://doi.org/10.1101/2020.03.23.20039446
- Centers for Disease Control and Prevention. Infection control guidance for healthcare professionals about coronavirus disease 2019 (COVID-19). https://www.cdc.gov/coronavirus/2019-ncov/hcp/infection-control.html
A pre-published study under peer review suggests particles of SARS-CoV-2 can linger on surfaces and travel in the air beyond six feet.
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