A complaint soon spotted? (7)

I believe the answer is:

measles

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'a complaint' is the definition.
(measles is a kind of disease)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for measles that I've seen before include "Morbilli is technical term for this illness" , "Viral disease once common in children" , "Rubeola" , "Contagious disease in children" , "Children's viral disease" .)

I've seen this clue in The Globe and Mail.

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