Transmission
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from the upper respiratory tract than from the lower respiratory tract and a shorter duration of viral shedding than persons with symptoms (Ip 2017). A review summarized the evidence of human SARS-CoV-2 transmission (Meyerowitz 2020): 1.
Respiratory transmission is the dominant mode of transmission.
2.
Vertical transmission occurs rarely; transplacental transmission has been documented.
3.
Direct contact and fomite transmission are presumed but are likely only an unusual mode of transmission.
4.
Although live virus has been isolated from saliva and stool and viral RNA has been isolated from semen and blood donations, there are no reported cases of SARS-CoV-2 transmission via fecal–oral, sexual, or bloodborne routes. To date, there is 1 cluster of possible fecal– respiratory transmission.
5.
Cats and ferrets can be infected and transmit to each other, but there are no reported cases to date of transmission to humans; minks transmit to each other and to humans.
Routes of Transmission SARS-CoV-2 is spread predominantly via virus-containing droplets through sneezing, coughing, or when people interact with each other for some time in close proximity (usually less than one metre) (ECDC 2020, Chan JF 2020, Li Q 2020, Liu Y 2020, Lu J 2020). Direct contact or fomite transmission is suspected and may occur in some cases. Sexual, fecal–oral, and bloodborne transmission are theorized but have not been documented (Meyerowitz 2020).
Respiratory transmission The upper respiratory tract is the usual initial site of viral replication, with subsequent descending infection (Wölfel 2020). The ideal transmission setting for SARS-CoV-2 is a crowded, closed and noisy space where people must shout to communicate. Shouting or speaking loudly emits a continuous flow of large droplets or fine aerosols laden with virions. Although aerosol lingers in the air for minutes, capable of infecting people at a distance, the ideal transmission setting (the ‘SARS-CoV-2 jackpot’ from the virus’s point of view) are people shouting at one another at a short distance, inhaling deep into theirs lungs the exhalations of the person they are speaking to/shouting at for 5, 10, 20 minutes or longer. Noisy machines, loud music or high spirits during exuberant gatherings in crowded and closed environments are there-
COVID Reference ENG 006.9
