The Widal test is one method that may be used to help make a presumptive diagnosis of enteric fever, also known as typhoid fever. Developed in 1896 and named after Georges Ferdinand Widal, who introduced it, the method relies on a reaction in a test tube or on a slide between antibodies present in the infected person's blood sample and specific antigens of S. typhi, which produces clumping (agglutination) that is visible to the naked eye. While the method is easy to perform, concerns remain about the reliability of the Widal test and studies of the assay is sensitivity and other measures of reliability have been disappointing. Besides cross-reactivity with other Salmonella species, the test cannot distinguish between a current infection and a previous infection or vaccination against typhoid. Widal is normally done after the 2nd week of fever.