A HEPA filter must remove at least 99.97% of aerosols 0.3μm in diameter. A filter which removed 99% and blows air 1% faster will remove just as much, or one which removes 50% and blows air twice as fast.
For recirculating air, all of those accomplish the same thing. Some of those have much higher noise, running costs, and general upkeep than others.
HEPA makes 100% sense for something where 100% of air passes through it. If you want an exhaust on a facility which handles biohazards, a vacuum cleaner kicking up dust, etc., sealed HEPA 100% is the way to go.
That's not what happens in a residential building, though. For that application, it's just bad engineering.
HEPA doesn't matter unless you have a sealed system. An open door or a cloth curtain means the 99.97% means nothing relative to 99%.
If you have two patients, they should both be isolated from each other. Which one gets the higher pressure, and which the lower?
https://de.wikipedia.org/wiki/Kontrollierte_Wohnrauml%C3%BCf...