To play devils advocate. If you ended up getting MRSA or something worse because you had to reuse an air boot that someone else has worn, then you would have been on here moaning about how the NHS cannot afford to give you a new air boot and how you have paid your taxes and NI all your life. Then someone else would moan about how NHS CEO's cannot sort out something simple like infection control. By the way it wouldn't be H&S, it would be infection control.
Those air boots are not designed to be sanitised. How do you propose to sanitise them? Autoclaving them would probably melt them or affect the structural integrity. Sometimes the cost of a disposable is cheaper than a reusable item in the long run. Work out the risks of someone else contracting MRSA/ESBL/PVL... chose what bug you like, and the costs of eradicating such infection and a disposable boot doesn't seem like such a bad idea.
Certainly I wouldn't want to re-use the boot you had on your foot for god knows how long. Worn in god knows what conditions. You may be a very clean person, but there are some disgusting folk out there. Trust me, I have had to go out on home visits.
Damned if you do, damned if you don't. You just cannot keep some folk happy.