I did a quick read-through of the U.S. Centers for Diseae Control website dealing with avian flu. Here:CDC flu webpage
According to this generally reliable source, no sustained human-to-human transmission of avian influenza (bird flu) has been documented yet. If that's true, then banning concerts and sporting events wouldn't make much difference in the spread of this disease - unless there are a lot of birds sitting in with the humans in the audiences. Reminds me of the universal advice for dealing with emergencies:

When in danger or in doubt

run in circles, scream and shout.