What is known: The virus is spread through human to human transmission. Asymptomatic cases are occurring and can be infectious. Two studies indicate that the most infectious period may actually be the first four days or so after exposure. Researchers found very high levels of the virus in upper respiratory tract samples before clinical symptoms occurred.[1,2]

What is unknown: All modes of transmission for COVID-19 have yet to be established.

However, current epidemiological evidence supports aerosol transmission of COVID-19. Aerosols, particles suspended in air, can be transmitted by an infected person through breathing, talking, coughing, and sneezing.[3] They can also be generated during medical procedures such as intubation and bronchoscopy. Particles vary in size; larger aerosol particles can remain suspended in the air for several minutes, while smaller or lighter ones can linger in the air for hours and travel through the room and ventilation systems. Perfume spray demonstrates the extent of aerosol distribution as it can be smelled from a distance for quite some time as the particles disperse throughout the room.

Similar to SARS (severe acute respiratory syndrome), researchers have found that SARS-CoV-2, the virus that causes COVID-19, can survive and stay infectious in aerosols for at least 3 hours.[4] SARS-CoV-2 can also survive on surfaces for an extended period of time. For example, genetic material from SARS-CoV-2 was detected on a number of surfaces in the Diamond Princess cruise cabins of both symptomatic and asymptomatic infected passengers 17 days after they vacated.[5] Asymptomatic virus shedding and viability in the air and on surfaces may explain the rapid person-to-person transmission. As such, all contact and airborne precautions must be maintained to protect healthcare workers.

[1] Woelfel, Roman et al. Clinical Presentation and Virological Assessment of Hospitalized Cases Of Coronavirus Disease 2019 In A Travel-Associated Transmission Cluster. MedRxiv, Cold Spring Harbor Laboratory Press, 2020. https://doi.org/10.1101/2020.03.05.20030502

[2] Nishiura, Hiroshi, et al. Serial Interval of Novel Coronavirus (COVID-19) Infections. International Journal of Infectious Diseases, Elsevier, 2020. https://doi.org/10.1016/j.ijid.2020.02.060

[3] Jones, R.M. and L.M. Brosseau, Aerosol transmission of infectious disease. Journal of Occupational and Environmental Medicine, 2015. 57(5): p. 501-8.

[4] N van Doremalen, et al. Aerosol and surface stability of HCoV-19 (SARS-CoV-2) compared to SARS-CoV-1. The New England Journal of Medicine, 2020. DOI: 10.1056/NEJMc2004973.

[5] Moriarty, et al. Public Health Responses to COVID-19 Outbreaks on Cruise Ships — Worldwide, February–March 2020. MMWR Morb Mortal Wkly Rep. DOI: http://dx.doi.org/10.15585/mmwr.mm6912e3