Personally, I believe that these stories get blown out of proportion simply because they make 'sensational news'.
(And they kill millions of birds when they do happen.)
The problem is real in the commercial poultry business because of the deplorable conditions under which most operate.
Overcrowding, unnatural diets, synthetic inputs, to name just a few.
Pandemics are a sign of an out-of-balance system.
The
permaculture methods of raising poultry bypass many of the health issues that plague BigAg.
BigAg does practice the "all-in/all-out" system, which helps them. As small growers, we
should do the same,
to an extent: Don't just add new birds to your flock at once. Keep them apart for a week or two to determine that they are healthy before stuffing them into your flock's coop.
Sadly, as small growers, our biggest threat is the State/County Poultry Inspector. He wants to 'help' you by examining your flock. But, he just left somebody else's coop with
chicken shit, bugs, and who knows what else on his
boots and cuffs. Your healthy flock could be at risk, after his 'help'.
Sunshine, fresh air and a natural diet of insects and fresh greens should put you far ahead of the commercial grower.
Be cautious when adding new birds. If you do have a sick bird, quarantine it apart from the healthy birds.