Nevertheless, food and water contamination might be good enough for the terrorist, who may simply want to cause panic or make the nightly news. Not all biological agents are created equal. If we examine the agent lists developed by proliferators during the cold war era, and even before, we see that most programs eventually focused on 10-15 agents. There is a reason the lists were so small. When one considers the hundreds of infectious agents and toxins, only a small subgroup has the physical and biological properties needed for a mass-casualty producing biological weapon.
Anthrax comes out high on everyone's list because the spore form of the organism is so very stable.
Some viruses require just a few organisms to infect and are so easy to grow to high concentrations that their relatively poor stability becomes less important. Two of the toxin families have been popular because of their extreme lethality or incapacitation effects. The point is that very few agents have the characteristics that make them good biological warfare, battlefield, mass-casualty weapons agents. However, terrorists don't have to deal with all the technical constraints intrinsic to the objectives of large national biological warfare programs. To illustrate this point, we did a theoretical analysis of 395 toxins, using the available data on their toxicity and applying mathematical calculations that were validated in field tests during the US offensive program in the 1960s.