The word unclean is a translation from the word akathartos. The overwhelming number of times the word is used in the New Testament, it is to describe the unclean spirits that Jesus would cast out (Matt. 10:1; Mk. 1:23; Luke 4:33, and many others). It is used several times in Acts this way, and also in the book of Revelation. But in the book of Acts, it is used to describe the unclean animals that were shown to Peter as emblematic of the Gentiles (Acts 10:14, 28; 11:8), who were now to be accepted as clean.
In 1 Cor. 7:14, Paul uses the word to describe the condition of children when both parents are non-believers. He also describes pagan idolatry this way, telling the Corinthians to come out from the idolatry of the pagans, not touching “the unclean thing” (2 Cor. 6:17). And last, he tells us in Eph. 5:5 that “no whoremonger, nor unclean person, nor covetous man, who is an idolater, hath any inheritance in the kingdom of Christ and of God.” While it is clear that this is describing moral uncleanness, we should not eliminate the consideration of physical filth. When Jesus cast out deaf and dumb spirits, He was casting out spirits that made the possessed person deaf and dumb. We should at least consider this as a possibility with unclean spirits as well — people who live in absolute physical squalor and filth have a serious spiritual problem as well. And this goes together with moral uncleanness.