structure "risk of the diseases returning"

[Tvita]

Could someone please explain to me the selected structure in the sentence below (from grammatical point of view of course ) ?

If the number of parents choosing not to immunise increased, there would be a similar increase in the risk of the diseases returning.

[RonBee]

The diseases that have been suppressed up until now would be more likely to return (come back).

[susiedqq]

in the risk of the diseases returning.

in / risk
the

of / diseases returning
the

[RonBee]

I managed to answer a question that wasn't asked.