(Not a teacher)
I wouldn't use "cut off" in place of "isolate" in this instance, although one of its meanings is certainly "to isolate." "Cut off" strikes me as beng more dramatic, and is often used in a military context:
Our regiment was cut off from the rest of the force by a sudden enemy attack.
Let's cut 'em off at the pass! (A famous expression from old cowboy films)
To "cut off the patients" almost has a cruel connotation.
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