This is one of those rare exceptions.
affect, the noun, is
used in psychiatric medicine (and similar lexical fields) to mean
"feeling tone", "attitude", "emotional response" -- that sort of thing.
the affect, stress on the first syllable.
There is nothing here to say, or even suggest obliquely, that the patient had an effect on anything, so
effect has to be ruled out. Aside from this specialized use as a noun,
affect should be thought of as 99.9% a verb.
CJ