The Uncleanness of the Disbeliever is Spiritual

Question :

We work with people who have no religion, who worship fire and the cow, and Allah has said about them that they are unclean and impure. What is the nature of this uncleanness? Should we avoid them and not shake their hands? And how, if they are unclean, can we work with them? Do the things they touch with their hands become unclean, bearing in mind the fact that they work in places of business and so they have relations with society? I request clarification.

Allah, the Most High says:
Verily, the Mushrikun (polytheists, pagans, idolaters, disbelievers in the Oneness of Allah and His Messenger, Muhammad) are Najasun (impure).

And regarding the hypocrites, He says:
So turn away from them. Surely they are Rijsun (i.e. Najasun - impure because of their evil deeds).

So Rijsun is Najasun; but their uncleanness is spiritual, which is their harmfulness, their evil and their corruption. As for their bodies, if they are clean, it is not said of them that they are physically unclean. Therefore, it is permissible to wear the clothes which they have worn, if it is known that they (the clothes) are clean, except those which have been in contact with their private parts, if they do not protect themselves from urine, especially if they are not circumcised. Likewise, if they are in contact with unclean things, such as by cooking pork, manufacturing alcohol and working with them. As for shaking their hands, and using the things which they manufacture, there is no objection to that, because the Messenger and his Companions, may Allah be pleased with them, used to utilize what the disbelievers had made or woven as long as it was known that they were clean; and the fundamental status of things is cleanness.

Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 1 Pages 270-271