How did my saliva test show up positive for cocaine when I didnt do cocaine

I had a saliva test and they said it came back positive for cocaine and I have not touched the stuff in years, what would make it positive?

I believe they used to use Cocaine leaves in Coca-cola. I believe they still do, but it's been heavily modified for "Civilian use" if that term makes any since. Supposedly, there are still trace elements of Cocaine in the drink, but only on a molecular level so it shouldn't really come up. but, it might still. On top of that, I know for a fact, Poppy seed bagels can give you a false positive for marijuana. Perhaps it was something you ate prior to the drug test?
Either way, I agree with rob, you should demand more testing if indeed you have not been doing drugs.

Screening tests produce more false positive results, they're used because they're less expensive. Demand a more accurate test.