Re the link all the way back to last summer:
"The studies referred to focus on masks as preventatives to catching influenza etc. As discussed here before, masks are essentially useful for checking transmission by the mask wearer themselves by means of preventing the wide expression of respiratory droplets (which are charged with viral and bacterial mater.) through coughing or sneezing.
-There's adequate Empirical evidence that this is the case, as here where oral bacteria colonise around the droplet destination. Virus of course won't grow in agar but need to enter a cell to replicate"