Single instances of infectious disease? (8,5)

I believe the answer is:

isolated cases

I'm a little stuck... Click here to teach me more about this clue!

'infectious disease?' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'single instances' is the wordplay.
'single' becomes 'isolated' (I've seen this before).
'instances' becomes 'cases' ('case' can be a synonym of 'instance').
'isolated'+'cases'='ISOLATED CASES'

'of' acts as a link.

Can you help me to learn more?

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

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.