In olden days people used to clean their hands and legs before they enter into their houses. They used to change the dress and then only they used to eat. These days we feel these are all not required. But those habits are good and if we follow them we will be safer.
But overdoing is not good. Cleaning a cleaned vessel, again and again, washing the hand every time after shaking hand with somebody, may not be required. This over cleanliness is a disorder, I feel. But taking correct precautions and observing cleanliness and maintaining hygienic condition can't be a psychological disorder.
"If you don't understand my silence, you will not understand my words"
Knowledge is power.
My conclusion would be that in this world the norms for routine transactions are set & anything beyond this would be considered as different & unusual for others. The extreme phenomenon of over cleanliness may be one of its kinds wherein the practitioner would be looking to the outside world from a different view point with some sort of allergic to even those which may not prove to be harmful like restricting to visit the hospitals etc.
The mentality of an individual seems to be over cautioned here so as to keep him or herself safe from the unrecognized living world of bacteria & diseases. I don't feel that this is something which we can refer to as "psychological disorder".
Each one of us is afraid of something which we are not aware of & so is the case here but for the sake of entertainment & nothing else.
Thoughts exchanged is knowledge gained.
However, it is always good to keep oneself neat and clean; prevent the infections and diseases prevalent in society but over cleaning is wasting the precious water, which the world is already short of, and it is compulsion under the psychiatric disorder which is Obsessive-Compulsive Disorder that force a person use extra water and yet not satisfied!