Agree w Dr. Lutwig. It depends on where you live. Since 1997 there has been 1 us outbreak of avian influenza a (h5 n2) from 1 farm. There have been sporadic outbreaks of the low pathogenic form of avian influenza a. If you don't live in areas where the avian flu has occured - don't know of any reason not to keep chickens. My brother continues to keep his chickens.
The avian flu H5N1. Is the variety that has been able to 'jump' to humans. It does not exist in the western hemisphere.