OK, call the American Association against Acronym and Abbreviation Abuse (the AAAAAAA) on me.
There are a number of acute pathologies that may resemble simple treat-at-home acutes that we really would not wish to miss.
Epiglottitis (resembling Croup or Pharyngitis)
Periorbital/Orbital Cellulitis (resembling a nasty case of Conjunctivitis)
Keratitis (resembling Conjunctivitis)
Uveitis (resembling Conjunctivitis)
Sepsis & Meningitis (resembling other common febrile illnesses, & Fevers of Unknown Origin)
Measles (presenting prior to its characteristic rash as conjunctivitis & non-specific upper respiratory illness)
I could make a much longer list, & may visit some additional entries in the future, but these are relevant to the pathogens I’ve addressed so far, and are plenty enough for one essay.