They know the problem; irritable bowel, but not what causes it. That's why they call it a syndrome and not a disease.
It's the same with AIDS vs HIV infection. AIDS: we don't know what causes it, but it is acquired immunodeficiency. HIV: it's a disease caused by this virus.
It's the same with AIDS vs HIV infection. AIDS: we don't know what causes it, but it is acquired immunodeficiency. HIV: it's a disease caused by this virus.