Where you're most at risk of COVID-19

 
It's very similar to Legionnaires' disease in how it's spread.  Legionnaires' also caused pneumonia-like symptoms that led to death in the same way Covid-19 does.

Now they're saying Covid-19 is an air-borne virus, even more than a 'by touch' contamination and spread. Is that an endorsement for masks, or what?

It also  explains why people on aircraft are easily infected: the circulating cabin air is no longer exhausted from the aircraft 'every 3 minutes' like it used to be.  The airlines rely heavily on hepa-like filters to keep the air clear of major particles.  So  do cruise ships.  But those filters cannot  filter out the small particles that carry Covid-19 virus.

Legionnaires' also was contracted from outside sources like pools and spas and hot water tanks that hadn't been drained or cleaned in many years.  Then it was spread from person to person indoors through ventilation systems.  And it also  hit the elderly and those with 'pre-existing' conditions harder than most.

Here's an article of how group-gatherings are the deadliest sources of all - and why being outdoors is safer than being indoors with people:

Quote from article:
"Ventilation seems to play a role and what that means is that transmission is occurring via droplets in the air that people are inhaling or somehow picking up," said Marr.

"The fact that ventilation seems to matter strongly suggests that there is transmission happening through the air."
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Canada is slowly reopening — and new research reveals where you're most at risk of COVID-19

https://www.cbc.ca/news/health/coronavirus-canada-spread-risk-covid-1.5572505