prolonged, inveterate, confirmed, habitual, progressive, addicted, degenerative, acute, debilitating, recurrent, more...

acute, temporary, transient, episodic, intermittent

cancer, diabetes, asthma, arthritis, obesity, heart disease, Alzheimer's disease, kidney disease, more...

more, acute, severe, active, simple, certain, less, common, local, mild, very

not going away,   never goes away,   slow infection,   persistent pain,   long sufferers,   ongoing problem,   does not go away,   cannot get rid of,   over a long time,   doesn't go away