Sorry my mistake. its 39 categories not 30 lol. spelling mistake.
The AMA (American Medical Association) Published an article on this some years back, i friend sent me a copy of the Page with the information on it stating that there are 39 Major disease categories known to man.
I've lost the fax as this i received many years ago, but i will contact him or search the AMA-Journals to see if i can find the exact details.
In the meantime, somebody told me that Doctors have a form where they ask you for what kind of diseases you have or something? I doubt live in America so i obviously dont know anything about this, but maybe you could grab a copy of the form if you like in the US or ask a doctor?
I'll let you know my findings