I don't know if I'll ever use this concept - Awful Hospital is becoming pretty crowded as it is - but early in the series I considered that the actual symptoms of illness might have associated entities. Fever and Chills in the lower right were the first two I came up with.
We actually haven't seen any diseases themselves "embodied" in Awful Hospital, so there's still room for beings like these to be canon. I considered maybe a disease manifests as a being - so there might be a creature that physically represents a Flu - but the disease in turn employs some "symptoms" as underlings.
This is all completely speculative.