There are routine protocols to keep health care workers from infecting patients. This is common, because the problem is a very common one. The stuff that lives

There are routine protocols to keep health care workers from infecting patients. This is common, because the problem is a very common one. The stuff that lives on a healthy nurses's hands may do no damage there, but would do terrible damage if it could invade a patient who's weak from yesterday's operation. The same applies to the common cold, to whatever the nurse may have picked up while treating another patient half an hour ago, and many, many other varieties of the same hygiene problem.