Typhoid and Paratyphoid Enteric Fevers - Diagnosis

Diagnosis of Salmonella infection is undertaken by

a) Isolation of Salmonella -

• Salmonella isolated using blood culture, organisms are isolated from blood stream at all stages of infection
• Salmonella species are isolated mostly from 2nd week and 3rd week from stool and urine samples respectively.
• Faeces and Urine are centrifuged and the deposits are enriched in Selenine F broth followed by inoculation in to Selective media Deoxycholate Citrate Agar (DCA)
• The colonies are tested for presence of Salmonella 'O' and 'H' antigens by slide agglutination test, followed by biochemical testing.

b) Widal test : -

• Widal test is done to detect Salmonella antibodies in the blood of infected person. Specific O and H antibodies of Salmonella are detected in blood.
• Detection of Vi antibodies in the serum is diagnostic for Salmonella chronic carriers.
• Four fold increase in antibody level is used for confirming Salmonella infection.