If you are referring to nouns and have already started the sentence with a plural construction, why would you use the singular form in your parentheses? I don't know what ear sticks are, so let me use a more understandable (for me) example. All professionals entering the court (lawyers and prosecutors) should ensure that they are dressed appropriately .
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AnonymousAll pools (serum and ear stick) tested PCR negative.Correct as you have it above IF you would normally use the nouns 'serum' and 'ear stick' with 'pool', thus, if you wrote it all out:
AnonymousGranted, it is a strange way to phrase it, but that is essentially what we're writing with ear sticks and serum, I think.Yes, the grammatical structure is essentially the same.