1. infection, 2. close contact, 3. closed quarters, 4. viral load
It is not so striking that health care workers might be infecting each other at greater rates than the general population. A large population study in NY state this past spring, back tracing infections, found that 80% of infections arose from contact either in the home (60%) or a healthcare/nursing home setting (20%). Those settings have items 1 through 4 more often than public venues when folks are out and about doing their daily business.
Uh-huh.
Now do that cruise ship at the beginning of the crisis.