Use the following symptoms in a new game
Insomnia
Paranoia
Seizures
Insanity
Dysentry
Diarrhoea
Keep your virus spreading and eventually you will unlock the trophy
You should get a popup about the Public Defecation combo just before it pops
I had a hard time getting this one to pop. failed first try (Cure was completed) Second try, didn't get it until the cure was 90%. I also devolved all symptoms except Diarrhoea and Insanity as those are the only two you need. I thought maybe this would keep doctors from working too hard on the cure.