I've seen the idiom 'keeping well' being used to mean 'in good health' in some contexts where British English is expected. But Americans seem surprised by it. Is that idiom uncommon in American English?
only cont.: Reverso (see below) records it as of 'exclusively continental usage'.
De tuenda sanitate by Plutarch: "Advice about Keeping Well"
Plutarch had more than a casual interest in medicine, for, besides this essay on keeping well, his other works abound in references to the behaviour of the sick and their treatment, and the medical practices of his day.
You can say or ask how someone is keeping as a way of saying or asking whether they are well.
She hasn't been keeping too well lately...
The only cont seems to refer to the usage in the continent alone, so it's alien to NAmer. usage.