Sorry, but I won't be plugging any unknown usb drives into the ambulance's computer,
Even if Windows is banned from ER and ambulances to fix the security/virus problem, there's no way to expect anyone to know what to do with any material other than printed English text.
Admittedly, plugging an unknown storage device into a mission-critical system, regardless of operating system, is dangerous. Nevertheless, if a Windows system is configured properly, there's no reason why it is any riskier than plugging into any other OS-based system. But I digress...
Plain old .TXT files can be read on any OS. JPEG is natively supported on all OS's for image files. These days, Adobe PDF is ubiquitous enough to also be a universal standard for documentation. If you are concerned about Adobe Reader's security flaws, the free FoxIt PDF viewer is a simpler, and accordingly safer, alternative.