I will never buy those high percentages as an overall number for the country. Could be some regions are higher than others, but the entire US? No way, IMO.
In the entire five-and-a-half years that I have had chickens, there has been no respiratory illness in my flock. Doesn't mean there never will be, sure, but I do not buy started birds from anyone, not even chicks unless they come directly from a hatchery shipment or are hatched here from eggs from very reputable long time breeders whose culling practices I'm familiar with. Everyone who comes here must disinfect their shoes before stepping into the "chicken zone". It's not perfect, but I feel goes a long way toward preventing an outbreak. Other than wild birds, which I feel are not the main source of contamination anyway, nothing is going to have an easy time getting into my flock.
The only way you can know is to have your birds tested. That's really it. Practice the best biosecurity you reasonably can, err on the side of caution every time, and you go a long way toward preventing the transmission of disease.