Exposure Risk for Hepatits C?

I just read an article today in the Wall Street Journal that freaked me out. The article was about the transmission of Hepatitis C through shared cocaine straws. (In retrospect this makes perfect sense, but at the time I didn't consider it.) Several years ago I tried cocaine once at a party. That was my only experience with drug use, I snorted half a line, and I always regretted it. I don't remember if the straw was shared, but it probably was.

Can anyone out there give me a ballpark risk calculation associated with a single exposure?

[copyman]

if it was only one time the odds are like one in 100,000. you had no risk. go and enjoy life. if you still feel obsessed get tested.