Thread by @EricMeyerowitz

1/ Our comprehensive review of transmission of SARS-COV-2 is out in @AnnalsofIM with @AaronRichterman @RMKGandhi @PaulSaxMD

acpjournals.org/doi/10.7326/M2…

2/ We review environmental viability of virus in experimental and real world settings.

RNA reported in many real world studies, but at very low copy counts

Viable virus assessed for only rarely and in those instances only isolated occasionally, also at very low levels

3/ We review viral and host factors that impact transmission

Children under ten appear half as susceptible but relative probability of transmission from children compared with adults not well understood

Virus with D614G mutation is associated with higher in vivo viral loads

4/ Respiratory transmission dominant

Droplet vs aerosol model = oversimplification

That proximity is key determinant of transmission suggests relative importance of classical droplet mode, but in indoor environments w/ poor ventilation, can transmit at a distance thru aerosols

5/ Despite concerns about fomite transmission, there is no conclusive evidence to support this mode of transmission and if it happens at all is likely only responsible for a minority of spread

That said good hand hygiene is protective against acquisition of virus

6/ Some domestic pets can be infected but no documented transmission from domestic pets to humans. However, minks can be infected and there is documented transmission from minks to humans

7/ It was unclear for a while, but there is now conclusive evidence for rare vertical transmission

8/ There is no conclusive evidence for fecal-oral spread. There is currently one cluster report potentially caused by fecal-aerosol spread, though this is likely extremely unusual

There is no current evidence for sexual or bloodborne transmission of the virus

9/ The "period of infectiousness" is best known for immunocompetent adults who develop symptoms

Infectiousness peaks just before or right around symptom onset and declines quickly after, despite ongoing RNA shedding

10/ In patients with mild or moderate disease, infectious virus cannot be cultured after around 8 days of symptom onset.

In those with severe or critical disease infectious virus can be cultured a bit longer, with the latest isolation of infectious virus 20 days after symptoms

11/ Despite isolation of infectious virus, there are no documented late transmissions, after about a week of symptoms

12/ Heterogeneous transmission is the explanation for superspreading events, which are an important feature propagating the pandemic

The figure models heterogenous transmission. An index case transmits to 2 secondary cases; 1 has no other transmissions while other transmits to 4

13/ Outside of superspreading events the household is a key site for transmission. After superspreading events further transmission frequently occurs in households

14/ Conclusions