Pretty secure, so long as someone isn't out to get you individually:
What is discussed in terrorist training manuals, and what the CIA is worried about, is the use of contaminated food in targeted assassinations. The quantities involved for mass poisonings are too great, the nature of the food supply too vast and the details of any plot too complicated and unpredictable to be a real threat. That becomes crystal clear as you read the details of the different incidents: it's hard to kill one person, and very hard to kill dozens. Hundreds, thousands: it's just not going to happen any time soon. The fear of bioterror is much greater, and the panic from any bioterror scare will injure more people, than bioterrorism itself.