Advice if friend has symptoms

[neomneomneom]

Sisters close friend who she saw for a long dinner and drinks a few days ago has developed coronavirus-like symptoms.

Explained to sister that she and her family should self quarantine - she is unconvinced. Can anyone find any guidance anywhere please?

I think guidance is only to self isolate if you or your family display symptoms, not if you've been in contact with someone showing symptoms. Unless it's a confirmed case.

So isn't this how it spreads? Surely once you develop symptoms it's too late?