Do Dry Impurities Transfer
The specific impurity being referred in the question does not transfer after it dries, therefore there is no question of transference in this case. However, as a general rule, if any impurity, whether dry or wet, can be clearly seen or clearly felt being transferred (via colour, wetness, smell) then it should be washed and if not, then mere doubts should be ignored altogether.
If an impurity cannot been seen or felt clearly, then the person is under no obligation to search for impurity at microscopic level. Remember that Islam doesn’t require you to burden yourself beyond your capacity. Such impurity ( asked in the question ) after drying off, does not tranfer the way you are imagining therefore, all the things being touched would not be rendered impure automatically. It is also recommended to consult a professional who can deal with OCD related issues. There are sevaral techniques which a professional can teach that can gradually reduce the OCD realted issues.