It hasn’t been documented yet, sure, I’ll give you that. You and I both have no idea if it has happened already and the patients didn’t get tested or they didn’t go to the hospital or doctor with the bird flu. They might not have even realized they had the flu.
Some have figured out that you can threaten but they still won’t budge banking on the status quo bias to keep you with them. Even when faced with competitor pricing they won’t give a discount. Don’t even give them the warning, just leave. Be a well informed consumer.