Trying to find the title of a movie?

I would be delighted if I could find a movie my Mum and I remember but no one seems to have ever seen. We both remember it was black and white and I would say late 40's - Synopsis (as we remember it) is that a woman and her husband/brother go on holiday and he goes missing, everyone pretends that they never met him or had contact with him and in the end up she finds that he has been taken to a hospital run by nuns because he has a contagious disease and the government wanted to cover it up as there is some big event coming up in the country. Funnily my sister also says she remembers it and remembers a big spiral staircase (but this could be bogus). I have been looking for this movie for at least 10 years but to no avail......thanks