why might it be difficult for medical professionals to diagnose a specific illness
Medical diagnosis Diagnosis is often challenging, because many signs and symptoms are nonspecific. For example, redness of the skin (erythema), by itself, is a sign of many disorders and thus does not tell the healthcare professional what is wrong. Thus differential diagnosis, in which several possible explanations are compared and contrasted, must be performed. This involves the correlation of various pieces of information followed by the recognition and differentiation of patterns. Occasionally the process is made easy by a sign or symptom (or a group of several) that is pathognomonic.
Typhoid fever The cause is the bacterium Salmonella Typhi, also known as Salmonella enterica serotype Typhi, growing in the intestines and blood.[2][6] Typhoid is spread by eating or drinking food or water contaminated with the feces of an infected person.[4] Risk factors include poor sanitation and poor hygiene.[3] Those who travel to the developing world are also at risk[6] and only humans can be infected.[4] Diagnosis is by either culturing the bacteria or detecting the bacterium's DNA in the blood, stool, or bone marrow.[2][3][5] Culturing the bacterium can be difficult.[10] Bone marrow testing is the most accurate.[5] Symptoms are similar to that of many other infectious diseases.[6] Typhus is a different disease.[11]