Well i have my plans on how to survive but here are some casual ways for it to start.
Chemical spills
Airborne Toxins
Failed Drug expieriments(Ex T-virus)
Radiation mutation (Fallout 3 style.)
Screwing with DNA.
Mutated disease (Ex Quarantine movie)
Bio-toxin chemical release.
There are many more ways in which it could possibly start.
I know how to survive each and everyone of those.
1:Use a gasmask and dont touch spill.
2:Gasmask...
3:DONT TAKE THE DRUG FOR GOD SAKES!
4:Dont near anything radiated
5:shouldnt have to worry about unless you signed your life to science.
6:Stay away from dogs or animals during this period of time.
7:Gasmask.....
They are not all successful. But they may decrease your risk of falling victim. Those just tell good ways to not get infected by the disease. Not how to avoid Zeds.