Here is my first best thought: From a systems theory perspective, the good doctor has just been triangulated.
A tells B about C, rather than
A enabling C to tell B, or
B just telling C on her own steam, or
A telling B about his own anxiety pertaining to C.
Triangling happens all the time, and triangulation (where B gets choked) often. It's always an awkward and uncomfortable position to be in, and sometimes dangerous.
So prevention would have been good--seeing it coming and heading it off at the moment when the husband calls and begins talking about his wife. Unless she's on the phone with him, or next to him, or he says, "It's okay to tell her I told you."
If he didn't say that, then the physician might call back and get permission. If not granted, one might inform that handling that information con-fidere (with faith or care) would mean discussing important info and source of such with the patient/wife regardless.
Or, as you suggest, one might simply ask pointed questions of the patient from a position of undisclosed knowledge, and be enabled to get to the heart of things more quickly without seeming to violate anyone's confidentiality.
Thinking ethics in addition to systems theory: The rules of confidentiality are meant to protect privacy. If the physician has indeed been triangulated on grounds of confidentiality (with the husband-caller), whose privacy is potentially being violated here? Or whose counts for most?
The caller has some privacy rights, yes, but the call he initiated was meant to disclose private information of the patient-wife; and her interests now may well weigh more heavily than his.
I would think that the most important ethics issue in this scenario would not be potential violation of confidentiality but (mis?)prescribing on grounds of not violating confidences despite having obtained information that matters.
Analogy is that of having obtained knowledge of a pending disaster while illegally eavesdropping, and then deciding not to sound a warning since the data was obtained unethically.
, Rosemary Flanigan Chair