No matter what OS you choose it is vulnerable to viruses. You and I will agree that the odds are your Windows system is much more at risk by at least an order of magnitude. But the IA people who demanded that this system run antivirus are just as likely to demand that Linux run antivirus, simply because the vulnerability theoretically exists and making that demand fulfills their CYA requirements. I've worked on standalone Linux systems that IA demanded have antivirus.
> Either you own that decision, and as part of your support your tool provides the necessary antivirus and you also insure through testing configuration management that its configured appropriately, or you choose a different option up to an including writing your own system to manage the "time critical bits".
According to the article, the software runs on the user's hardware. While they certainly could have made a decision to provide their own controlled hardware, it's entirely possible that hospital was not open to that option for cost reasons, for IT management reasons, whatever.