A test to detect typhoid fever. A sample of the person’s blood is put into a solution containing typhoid bacilli, or anti-typhoid serum is added to a sample of bacilli from the person’s faeces. If the bacilli agglutinate, i.e. form into groups, this indicates that the person has typhoid fever. [Described 1896. After Georges Fernand Isidore Widal (1862-1929), French physician and teacher.]
An agglutination test for the presence of antibodies against the Salmonella organisms that cause typhoid fever. It is thus a method of diagnosing the presence of the disease in a patient and also a means of identifying the organisms in infected material.