Airborne Transmission

Last review completed on
April 10th, 2020
Therapy Description

Controversy exists regarding Airborne verses Droplet transmission of SARS-CoV-2

UMN CIDRAP Commentary regarding viral transmission:


    Clinical Circumstances
    List of Evidence/ Discussion

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    Argument against Airborne

    Argument for Airborne

    • A study published from the University of Nebraska Medical Center has raised concerns that COVID-19 may be an airborne pathogen
      • To improve UNMC's understanding of environmental transmission, researchers obtained surface and air samples in 11 negative pressure rooms where SARS-CoV-2 patients were being treated
      • All patients had mild disease, none required ICU care
      • 76.5% of patient personal items were positive for SARS-CoV2 by PCR
      • This included the patients BP cuff, pulse ox, nasal cannula, reading glasses, iPads, personal computers
      • 83.3% of patient cellular phones were positive
      • 64.7% of patient TV remote controls were positive
      • 81% of toilets were positive
      • 75% of bedside tables and bedrails were positive
      • 81.8% of window ledges were positive including ventilation grates
      • Air samples (in patient rooms) were positive despite being > 6 feet from the patient
      • Air samples taken outside of patient's negative pressure rooms in hallways were positive 66.7% of the time
      • Limitations:
        • While these studies identified viral RNA it should be noted that rtPCR is highly sensitive and it is unknown if this was merely fragments of viral RNA or infectious virus with viral activity
    • Another study by Liu et al collected 35 aerosol samples of three types of air samples from the ICU, CCU, and Floor from various hospitals throughout China. The samples collected were categorized as follows:
      • Aerosol samples of total suspended particles (TSP) with no upper size limit
      • Aerodynamic size segregated aerosol samples to determine the size distribution of airborne SARS-CoV-2
      • Aerosol deposition samples to determine the deposition rate of airborne SARS-CoV2
      • 21 samples had detectable virus with an average virus concentration (copies m^3) of 18.24 (range 1 - 113)
      • Of the 30 TSP samples, 16 samples (53.3%) had detectable virus with an average virus concentration (copies m^3) of 9.8125 (range 1-21)
      • Of the 2 Aerosol deposition samples, 2 samples (100%) had detectable virus with an average virus concentration (copies m^3) of 72 (range 31 - 113)
      • Of the 3 size segregated aerosol samples, 3 samples (100%) had detectable virus with an average virus concentration (copies m^3) of 27.3 (range 20-42)
      • This study was the first field report of the characteristics of airborne SARS-CoV2 in Wuhan.
      • The following additional details were also made:
        • Patient Areas
          • From Fangcang hospital the authors collected 5 air samples from 3 workstations, 4 (80%) of the samples had detectable virus with an average virus concentration (copies m^3) of 4 (range 1-9). One sample was also taken from a mobile toilet room which had a detectable virus concentration of 19
          • From Renmin Hospital the authors collected 3 air samples from three units and none had detectable virus. Aerosol deposition was positive in 2 of 2 samples with mean viral concentrations of 72 (range 31-113)
        • Medical Staff Areas
          • Viral particles were present in 10 of 13 (77%) of medical staff areas
          • Concentrations were highest in the Protective Apparel Removal Room (PARR) where 3 of 5 air samples had virus with mean viral concentration of 26 (16-42)
          • Of concern virus was present in both Male (concentration: 20) and Female (concentration: 11) changing rooms, the Medical Staff's Office (Concentration: 20), the meeting room (concentration: 18) and 1 of 2 warehouse samples (concentration: 21).
          • It was also present in the hospital hallway and dining room (concentration: 6)
          • Virus was present in the air samples taken from the hospital pharmacy (concentration: 3)
        • Community
          • Air samples were also taken from nearby community centers. No virus was detected at a nearby supermarket, doctors office, outpatient clinic hallways, or residential building.
          • Virus was detected in the air at a nearby department store (2 of 2 samples positive with concentrations of 3 and 11).
      • The authors suggested attention to the following elements:
        1. Proper cleaning of toilets (e.g. ventilation and sterilization)
        2. Use of personal protective measures such as masks by the general public
        3. Effective sanitation of high risk areas and use of high level protection masks for medical staff with direct contact with Covid-19 patients
        4. Awareness that the virus may be re-suspended from contaminated protective apparel surface to the air when taking off and from the floor surface with the movement of medical staff
      • Limitations:
        1. Small sample size
        2. Highest concentration of virus
    • A publication by Chia et al conducted by researchers from Singapore, University of Maryland, and Duke University conducted air sample evaluations
      • A study was done at the National Center for Infectious Diseases in Singapore in airborne infection isolation rooms (AIIR)
      • Six bioaerosol samplers were placed in each of the three AIIR to collect air samples at 3 different heights from the ground
      • 8-20 surface samples were also collected per room including air exhaust outlets and glass window surfaces
      • Samples were confirmed by rtPCR for SARS-CoV-2 envelop genes -AND- orf1ab assay to detect SARS-CoV2 from samples
      • All samples were ran in duplicate
      • Results:
        • Air samples were collected in 2 of 3 (66%) of samples collected. The average number of SARS-CoV-2 RNA copies per m^3 in air was 1306.8 (range: 916 - 2000).
          • Both patients with positive air samples had been ill for 5 days, whereas the patient with negative air samples had been ill for 9 days.
            • A recent study published in Nature on April 15, 2020 suggests studying viral shedding and transmissibility of Covid-19 identified that infectiousness begins 2.3 days before symptoms onset and peaks 0.7 days prior to symptom onset. Infectioussness declines quickly within 7 days and thus may provide new understanding for why the patient with an illness greater than 7 days had negative air samples.
            • These findings corroborate another study published in Nature from Wuhan that reports infectiousness declines significantly 8 days after symptom onset as live virus could no longer be cultured after day 7.
        • 17 of 30 rooms had surface environment contamination
          • The three most frequently contaminated samples were the Floor (65%), the Air Exhaust Vent (60%) and the Bed Rail (60%)
        • 65% of patients with less than 7 days of illness had contamination of "high touch" surfaces, whereas only 20% of patients with more than 7 days of illness had contamination of "high touch" surfaces.
          • High touch surface contamination peaked around days 4-5
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