Yeah, GUMSHOE is all about the little fiddly skills - due to their mechanic, it works out better than a traditional skill-points game.
In Mutant City Blues, there are the following medically related skills.
"Medic", a general ability to actually patch people up with first aid. If anyone's going to be a nurse or EMT or whatnot you probably do want a general skill like that.
Then they have:
forensic anthropology ("normal" forensics)
forensic entomology (bug specialist)
because mostly they're concerned with dead people, and then Chemistry as pseudo-related.
For a purpose built medical game I think extreme drilldown on medical skills is appropriate. I might do:
- Medic (for EMTs and nurses)
Technical: (cut ones that aren't needed - you say "occult plague" so who knows what might come in...)
- Anatomy (the body)
- Cytology/histology (cells/tissues) - might be more relevant in a disease scenario
- Neuroscience (nervous system)
- Emergency Medicine (for keeping victims actually alive via workarounds)
- Pharmacology (drugs)
- Toxicology (drugs, bad) - may or may not be needed
- Surgery (operating) - there are subspecialties but don't sound like they're relevant here
- Forensic Pathology (cause of death)
- Forensic Entymology (bugs & the dead) - maybe needed
- Forensic Anthropology (the long dead) - probably not needed unless they have bones of victims of a similar plague in the 1300s or whatever
- Forensic Archaeology (grave sites) - almost certainly not needed if they're stuck there
- Forensic Dentistry (teeth) - almost certainly not needed
- Medical History - useful if the occult part means that knowledge of past plagues, or vaguely mystical pseudo-medical mumbo jumbo about humors and whatnot is relevant
I could be more specific if I knew if ancient/historical/mythical stuff is relevant at all to the occult plague or whether it's just a new thing, and how much working on dead bodies will be relevant, and how much trying to tactically keep sick people alive is a focus. I think forcing a balance between intervention to keep people alive and "solving the root cause of the problem" would be compelling.