The Widal Blood Test is used to quickly diagnose enteric or typhoid fever. Enteric fever is caused by a species of bacteria called Salmonella enterica or Salmonella enterica serovar Typhi. Enteric fever may result 8-48 hours after infection by S. enterica and last 2-5 days. It usually clears away without significant medical intervention. However, it can also cause life-threatening complications. It measures agglutinating antibody levels against O and H antigens. The Widal test is positive after the tenth day of the disease and may be false positive if an individual previously received a TAB vaccine.