Dr. Sudhir Mehta shares his expert comments on yet another paper published in NEJM that throws light on the transmission routes of the of both SARS-CoV-1 and SARS-CoV-2 viruses.
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SARS coronaviruses- Viable in aerosols for hours and on surfaces for days*
To compare SARS-CoV-1, which caused a multi-country outbreak in 2002 to 2003, and SARS-CoV-2, which causes COVID-19 (now a pandemic), researchers evaluated stability of the two viruses in aerosols and on various surfaces and estimated decay rates. They aerosolised the viruses (creating particles <5 μm) using inoculum that resulted in values similar to those found in human respiratory tract samples.
After aerosolisation, viable SARS-CoV-2 virus was detectable throughout the 3-hour experiment; infectious titre dropping from 103.5 to 102.7 TCID50 (50% tissue-culture infectious dose) per litre of air. SARS-CoV-2 was detectable after 72 hours after application to plastic and after 48 hours on stainless steel, although titres dropped. Survival was shorter on cardboard (no viable SARS-CoV-2 after 24 hours) and copper surfaces (no viable SARS-CoV-2 after 4 hours). The half-lives of the two viruses in aerosol were similar (1.1 to 1.2 hours). Survival of both viruses was similar except SARS-CoV-2 survived longer than SARS-CoV-1 on cardboard.
Dr. Sudhir Mehta’s comment
Clear understanding of transmission routes is essential to contain spread. Previous epidemiologic observations and laboratory studies suggested that SARS-CoV-1 was transmitted primarily by close contact, probably via droplets, but transmission via aerosols and fomites also occurred. Nosocomial and superspreading events during the SARS epidemic were linked to aerosol-generating procedures. A recent study showed that SARS-CoV-2 can contaminate multiple surfaces in rooms occupied by patients with active infection (NEJM JW Infect Dis Apr and JAMA 2020 Mar 4; [e-pub]).
The current authors observe that the stability of the two viruses is similar under the laboratory conditions they used and suggest that differences in epidemiology reflect other factors such as high SARS-CoV-2 loads in the upper respiratory tract and the potential for infected persons to transmit the virus while asymptomatic. They conclude that transmission of SARS-CoV-2 by aerosol and fomites is plausible, although the artificial nature of the aerosol must be noted and the relative contribution of each potential route to overall transmission in various settings remains unknown.