Hospitals are also famous for spreading infections around, let's not forget that.
But now we know despite the hospitals' efforts to stop infections, they can not stop the infections from being transferred by the ambulances and EMS providers. When there is a weak link in the patient care system as it now appears ambulances are, no matter how much the hospitals try, infections will still roll in. This definitely explains a lot especially in LTC where transfer by ambulance is so frequent.