If a couple don't currently have other sex partner, and the wife hasn't infected cmv by lab test, can we assume the husband hasn't infected cmv either

I wouldn't: CMV is a viral infection that most of the population will eventually have. Once they have it & become immune, they are not contagious. It has little significance unless a pregnant woman acquires it & passes it to her fetus. It is most often acquired casually from public sources, but could pass sexually.A male partner who is CMV positive likely had it years before & would not be expected to pass it