Is it correct to paraphrase "the most" as "one of the most"
Solution 1:
This doesn't convey the same thing.
"[...] PCP was the most opportunistic infection."
This means that PCP was the top-most, number one. There are no infections that are more opportunistic than this one.
"[...] PCP as one of the most predominant opportunistic infections."
This means that PCP was among the top, but usually means that it wasn't #1. Might be #3 or #5. Still a lot, but not the most.
Depending on your goals, it might be alright to use the latter phrase. Just know it doesn't mean the same thing.