Salmonella typhi, the causative agent of typhoid fever, is approximately 50,000 years old. Assays that identify Salmonella antibodies or antigens support the diagnosis of typhoid fever, but these results should be confirmed with cultures or DNA evidence. The Widal test has been the anchor for diagnosis of typhoid fever for decades. It is used to quantify agglutinating antibodies against H and O antigens of S. typhi.