Fever is recognized as a manifestation of illness. Physicians in the early 19th century were able to distinguish between several febrile illnesses such as typhoid and typhus on clinical grounds. The benefit of measuring temperature to differentiate between diseases was first recognized by Wunderlich, a German clinician, in 1868. The cause of a fever will usually become evident within 1-2 weeks or it will spontaneously resolve. The challenge arises with the problem of diagnosing prolonged fever.