pf2e.fyi
From Pathfinder Lost Omens Ancestry Guide, which isn't enabled.

Plague Sniffer

FEAT 5
Prerequisites longsnout rat heritage

You can sniff out the pungent tang of disease. When you detect a creature by scent, you can also detect if that creature is suffering from a disease at a non-carrier state. If the disease is particularly subtle, you might need to attempt a Perception check against the disease's DC (subject to the GM's discretion).

Pathfinder Lost Omens Ancestry GuideOGL