When mucking about it filthy environs, you expose yourself to all manner of
hazards; among them is the virulent disease known as Filth Fever, which taps
your constitution and dexterity, and makes you shiver and sweat. Unlike with
some other maladies, the mere passage of time will not resolve filth fever.
The attentions of a professional healer are required to cure the disease. If
you haven't a friend capable in this regard, many clerics and druids in
temples about the realms can aid you, in return for a donation to their
church. Ask them to 'heal' you.