What is the ruling on obsessive thoughts regarding cleanliness resulting from observing unhygienic habits, and what should be done about it?

You must disregard these whisperings and pay no attention to them. The default state of people who visit you is purity. Therefore, do not purify anything they touch or sit on. Rather, act upon the certain principle, which is purity, until you gain absolute certainty to the contrary. Deal with all people, in all situations, based on the ruling of purity for everything connected to them, touched by them, or sat upon by them, and do not rule any of that as impure. The droppings of birds whose meat is permissible to eat are pure, according to the preponderant opinion. A small amount of blood is excused by the majority of scholars. The default state of the bathroom floor is purity unless you are certain of its impurity. So, cast off these whisperings and pay no heed to any of them.