Generally there is an "MCI kit", which has a form that can be attached to the patient (an elastic band around the wrist or ankle, generally). That form will contain whatever information we know about the patient, interventions thus far, etc. It stays with them throughout the process (in the triage and treatment areas, to the OR, etc). That being said, documentation is often a tertiary concern at best in large scale events like this.
As far as infection control goes, the OR is obviously using standard sterile procedures. In the ER, infection control is mostly "changing your gloves a lot" (be sure to put on two pairs, any only change the top pair, as your hands are going to get really sweating, and putting a new pair of gloves on your bare hands is going to be impossible).