Could be dry runs, but a major bio attack would involve many thousands of people at once (anthrax, toxins in the water, etc.).
An exception would be smallpox (shudder). That would start small, probably in several areas at once.
re- illnesses: then again, jihadis delivering food to restaurants or working in them could do quite a bit of damage on a fairly small scale. I recall reading how they could spread e coli on food----well- working in a fast food restaurant- all they would have to do is neglect to wash hands. Didn't one of the jihadi threats say something about McDonalds and Burger King? (Not to get too paranoid.) Interestingly, the ME who was taking the CDL course with my son said that he would NEVER eat in a fast food restaurant....interesting.