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Is Covid-19 droplet or air-borne infection?

Asked by Anup 

Respiratory droplets are referred to droplet particles > 5–10 μm in diameter. It has been regarded that COVID-19's spread is primarily with respiratory droplets and there is controversy about airborne transmission (droplet particles < 5 μm in diameter or droplet nuclei).

A commentary published by Greenhalgh T, et.al. on May 1, 2021 in Lancet has provided 10 scientific reasons in support of airborne transmission as a predominant mode of transmission of SARS-CoV-2 which seems to be very convincing:

  1. Long-range transmission observed at super-spreader events.
  2. Long-range transmission has been reported among rooms at COVID-19 quarantine hotels, settings where infected people never spent time in the same room.
  3. Asymptomatic individuals account for an estimated 33% to 59% of SARS-CoV-2 transmission, and could be spreading the virus through speaking, which produces thousands of aerosol particles and few large droplets.
  4. Transmission outdoors and in well-ventilated indoor spaces is lower than in enclosed spaces.
  5. Nosocomial infections are reported in healthcare settings where protective measures address large droplets but not aerosols.
  6. Viable SARS-CoV-2 has been detected in the air of hospital rooms and in the car of an infected person.
  7. Investigators found SARS-CoV-2 in hospital air filters and building ducts.
  8. It's not just humans — infected animals can infect animals in other cages connected only through an air duct.
  9. No strong evidence refutes airborne transmission, and contact tracing supports secondary transmission in crowded, poorly ventilated indoor spaces.
  10. Only limited evidence supports other means of SARS-CoV-2 transmission, including through fomites or large droplets.
Greenhalgh T, Jimenez JL, Prather KA, Tufekci Z, Fisman D, Schooley R. Ten scientific reasons in support of airborne transmission of SARS-CoV-2. Lancet. 2021 May 1;397(10285):1603-1605. doi: 10.1016/S0140-6736(21)00869-2. Epub 2021 Apr 15. PMID: 33865497; PMCID: PMC8049599.