The primary result of an effective aerosol cloud is simultaneous infections among all those who were exposed to a sufficiently dense portion of the cloud. If the agent is contagious, the disease will then spread. In addition, agents that can survive for a long time in the environment will eventually settle, contaminating the ground, buildings, water and food sources, and so on. In some cases, these sediments can form another dangerous aerosol cloud if they are disturbed. The interest of terrorist groups in biological weapons is no surprise.
Biological weapons have a number of very attractive features for terrorist uses.
Their killing power can approach that of nuclear weapons. They are relatively inexpensive to make. A small-scale biological weapons attack using a common disease organism, such as tularemia or plague, can be masked as a natural outbreak. The effects of a biological weapons attack are not apparent for several days, allowing the perpetrator time to vanish. The raw material disease-producing strains of microorganisms is fairly easy to obtain.