Purpose serological test for enteric fever In and named after its inventor, Georges-Fernand Widal , is a presumptive serological test for enteric fever or undulant fever whereby bacteria causing typhoid fever is mixed with a serum containing specific antibodies obtained from an infected individual. In cases of Salmonella infection, it is a demonstration of the presence of O-soma false-positive result. Test results need to be interpreted carefully to account for any history of enteric fever, typhoid vaccination, and the general level of antibodies in the populations in endemic areas of the world. Typhidot is the other test used to ascertain the diagnosis of typhoid fever. As with all serological tests, the rise in antibody levels needed to perform the diagnosis takes 7—14 days, which limits its applicability in early diagnosis.
|Published (Last):||15 April 2012|
|PDF File Size:||7.49 Mb|
|ePub File Size:||6.11 Mb|
|Price:||Free* [*Free Regsitration Required]|
When facilities for culturing are not available, the Widal test is the reliable and can be of value in the diagnosis of typhoid fevers in endemic areas. Typhi 0 antigen suspension, 9, 12 S. Typhi H antigen suspension, d S. Paratyphi A 0 antigen suspension, 1, 2, 12 S. Paratyphi A H antigen suspension, a S. Paratyphi B 0 antigen suspension, 1, 4, 5, 12 S.
Paratyphi B H antigen suspension, b, phase 1 S. Paratyphi C 0 antigen suspension, 6, 7 S. Paratyphi C H antigen suspension, c, phase 1 Salmonella antibody starts appearing in serum at the end of first week and rise sharply during the 3rd week of endemic fever. It is preferable to test two specimens of sera at an interval of 7 to 10 days to demonstrate a rising antibody titre. Principle of Widal Test Bacterial suspension which carry antigen will agglutinate on exposure to antibodies to Salmonella organisms.
The main principle of widal test is that if homologous antibody is present in patients serum, it will react with respective antigen in the reagent and gives visible clumping on the test card and agglutination in the tube. Preparation of Widal Antigens H suspension of bacteria is prepared by adding 0. Standard smooth strains of the organism are used; S Typhi , O and H strains are employed for this purpose.
Procedure of Widal Test Place one drop of positive control on one reaction circles of the slide. Pipette one drop of Isotonic saline on the next reaction cirlcle. Pipette one drop of the patient serum tobe tested onto the remaining four reaction circles. Mix contents of each circle uniformly over the entire circle with separate mixing sticks. Rock the slide, gently back and forth and observe for agglutination macroscopically within one minute.
Add to each reaction circle, a drop of the antigen which showed agglutination with the test sample in the screening method. Using separate mixing sticks, mix the contents of each circle uniformly over the reaction circles. Rock the slide gently back and forth, observe for agglutination macroscopically within one minute. Pipette into the tube No. To each of the remaining tubes 2 to 8 add 1.
To the tube No. Transfer 1. Continue this serial dilution till tube no. Discard 1. Tube No. Now the dilution of the serum sample achieved in each set is as follows: Tube No.
Dislodge the sedimented button gently and observe for agglutination. No agglutination is a negative test result and indicates absence of clinically significant levels of the corresponding antibody in the patient serum. The sample which shows the titre of or more for O agglutinations and or more for H agglutination should be considered as clinically significant active infection. Example: In the above figure, titre is Demonstration of 4-fold rise between the two is diagnostic.
H agglutination is more reliable than O agglutinin. Agglutinin starts appearing in serum by the end of 1st week with sharp rise in 2nd and 3rd week and the titre remains steady till 4th week after which it declines. Limitations of Widal Test The Widal test is time consuming to find antibody titre and often times when diagnosis is reached it is too late to start an antibiotic regimen.
The Widal test should be interpreted in the light of baseline titers in a healthy local population. The Widal test may be falsely positive in patients who have had previous vaccination or infection with S.
Besides cross-reactivity with other Salmonella species, the test cannot distinguish between a current infection and a previous infection or vaccination against typhoid. Widal titers have also been reported in association with the dysgammaglobulinaemia of chronic active hepatitis and other autoimmune diseases. Occasionally the infecting strains are poorly immunogenic.
The World Health Organization WHO has said that due to the various factors that can influence the results of a Widal test, it is best not to rely too much on this test.
Widal test: Principle, Procedure, Results, Interpretation, Significance and Limitation
This test was devised by Frank Widal in Widal originally described the test to diagnose Salmonella enterica serotype Paratyphi B infection. Patients infected with S. Widal test is the most widely used diagnostic test for typhoid fever in developing countries.
Sponsored link The Widal test is a test procedure that involves mixing of the bacteria which cause typhoid fever to the blood consisting of certain antibodies taken from an infected person. It is an assumptive serological test used for undulant fever or enteric fever. When the Widal test is used to check of the presence of Salmonella infections, then it is a presentation of the occurrence of O-soma false-positive result. It is important to carefully and correctly interpret the test results as per the past history of enteric fever, the typical composition of antibodies in the general population living in the endemic regions of the world and typhoid vaccination. Another test which is employed to detect and diagnose typhoid fever is the Typhidot test. The other procedures that can be used to diagnose Salmonella typhi or paratyphi include options like urine, blood and stool cultures. It may be noted that such microbes make H2S from thiosulfate which can be effortlessly recognized on differential media like Bismuth sulfite agar.
Widal Test- Introduction, Principle, Procedure, Interpretation and Limitation
Widal test card or slide. Procedure of Widal Test Widal test can be done in two ways. One is rapid test on slide and another is tube test in which result may be obtained after one night of incubation. For Rapid Slide Test Clean the glass slide or test card supplied in the kit well and make it dry.
Widal Test : Principle, Procedure, Result Interpretation and Limitations
Laboratory diagnosis of enteric fever includes Blood culture, Stool Culture and Serological test. Widal test is a common agglutination test employed in the serological diagnosis of enteric fever. Antibodies in serum, produced in response to exposure to Salmonella organisms will agglutinate bacterial suspension which carries homologous antigens. This forms the basis of Widal test. The organisms causing enteric fever possesses two major antigens namely somatic antigen O and a flagellar antigen H along with another surface antigen, Vi. During infection with typhoid or paratyphoid bacilli, antibodies against flagellar antigen of S. Positive result is indicated by the presence of agglutination Absence of agglutination indicates a negative result.