Does SARS CoV-2 Spread Primarily by Droplet or Aerosol Transmission? Why Does It Matter?

Details

• Corporate Authors:
  Michigan State University. College of Human Medicine
• Description:
  On 2/1/2021, the American Industrial Hygiene Association (AIHA) issued a statement in conjunction with nine other occupational safety and health organizations titled Joint Consensus Statement on Addressing the Aerosol Transmission of SARS CoV-2 and Recommendations for Preventing Occupational Exposures. The premise of this document was that understanding the role of aerosol transmission of SARS CoV-2 is an important component of adopting appropriate worker and community protection strategies. Key points were: 1) "People generate aerosols while breathing, talking, singing, coughing, and sneezing in a wide range of particle sizes (0.1 to > 100 µm). Some of the larger-sized particles will rapidly settle while some will rapidly evaporate to smaller droplet nuclei. Particles less than 10 µm will take minutes and hours to settle, during which they can be distributed throughout a space by diffusion and air currents. 2) SARS-CoV-2 can remain viable in air up to and perhaps longer than 3 hours, thus someone located both near and far from an infectious source could inhale infectious SARS-CoV-2 particles. 3) The receptors for SARS-CoV-2 in the body (ACE2) are located throughout the respiratory system. People are capable of inhaling particles over the entire particle size range of aerosols, with larger particles more likely to deposit in the upper respiratory system and smaller particles having a greater probability of penetrating into and depositing in the lungs, bronchioles, and alveoli. 4) None of the modes of transmission - contact, droplet, airborne, and aerosol - should be ruled out, although inhalation appears to be more important than contact transmission. 5) We do not yet know what level or amount of virus is associated with transmission from person-to-person. Recent data suggest that viral RNA levels greater than 106 are more likely to be associated with culturable virus, and that people shed infectious virus for only the first 8 days after symptom onset. 6) So much of infection prevention and control is based on practices in healthcare focused on patient safety and now it is clear that public health efforts need to also be focused on worker safety in all industries." None of the above statements are particularly controversial. However, public health authorities, both the World Health Organization and CDC, while acknowledging the potential of aerosol transmission, maintain that "The principal mode by which people are infected with SARS-CoV-2 (the virus that causes COVID-19) is through exposure to respiratory droplets carrying infectious virus." CDC states that the control of certain bacteria (e.g., Mycobacterium tuberculosis) and viruses (e.g., rubeola, varicella-zoster) is based on their transmission through the air. However, CDC cites the epidemiology of SARS-CoV-2 to conclude that SARS-CoV-2 is more like other respiratory viruses than TB or measles and that SARS-CoV-2 spreads by respiratory droplets directly impacting the mucosa at close range rather than to individuals farther away or to individuals entering a space hours after a SARSCoV-2 infected individual left the area. Although aerosol transmission is recognized to occur, the situations when this occurs are not considered common (i.e., enclosed space, prolonged exposure as with singing, shouting or exercising, and inadequate air exchange). [Description provided by NIOSH]
• Subjects:
  Aerosols Communicable Diseases Occupational Health Respiratory System Respiratory Tract Diseases Safety
• Keywords:
  Coronavirus COVID-19 Disease Transmission Infectious Diseases Respiratory Diseases SARS-CoV-2 Surveillance
• Publisher:
  Michigan State University-College of Human Medicine
• Document Type:
  Text
• Funding:
  Cooperative Agreement
• Genre:
  Newsletter
• Place as Subject:
  Michigan ; OSHA Region 5
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-4
• Volume:
  32
• Issue:
  2
• NIOSHTIC Number:
  nn:20066653
• Citation:
  Project S.E.N.S.O.R. News 2021 Feb; 32(2):1-4
• Contact Point Address:
  MSU-CHM, West Fee Hall, 909 Fee Road, Room 117, East Lansing, MI 48824-1316
• Federal Fiscal Year:
  2021
• Performing Organization:
  Michigan State University
• Peer Reviewed:
  False
• Start Date:
  20050701
• Source Full Name:
  Project S.E.N.S.O.R. News
• End Date:
  20260630
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:17ed2960e5992904d6f9ee7a00f7ded32de1b6126d5108942b8fb22a1178b78c3108e701aa1a583445400286bc8a15281a2e76d48787ad4fe6d8628c5d5a9f70
• Download URL:
  https://stacks.cdc.gov/view/cdc/230944/cdc_230944_DS1.pdf
• File Type:
  [PDF - 126.32 KB ]