WIDAL TEST - WHY STILL WE DO IT ?*T.V.RAO, MARY MATHEWS NAVIEEN G GOWDA, DEEPA BABIN, SUGEESH SEBASTAIN

DEPARTMENT OF MICROBIOLOGY

TRAVANCORE MEDICAL COLLEGE, KOLLAM KERALA

The gold standard in diagnosis of Enteric fever remains when the pathogen can be recovered from the blood during the first 7-10days of illness. The Widal test continues to be a popular test done in many Developing countries as presumptive diagnosis of Typhoid fever. Although the test is no longer commonly performed in the developed countries, it is still in use in many developing countries where enteric fever is endemic with limited resources; however we require the use of rapid, affordable testing alternatives. For diagnosing a case of enteric fever, Widal test is the second most widely used test after blood culture. Widal test using antigen suspensions appropriate to the diagnosis of the prevalent enteric fever agents has been used either to compare paired sera or to test a single serum taken on admission to see significant antibody levels. In endemic areas, such as India the bacterial culture facilities are often unavailable or limited to teaching Hospitals and accredited laboratories. The blood culturing continues to be unpredictable proving sterile with uncontrolled, empirical use of Antibiotics in particular Cephalosporin group of Antibiotics. Howeverthe Widal test continues to be the most simple, over

utilized, specific diagnostic? Investigation tool available in the local Laboratories in developing countries. It is 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 of sensitivity and other measures of

reliability have been doubtful. Besides cross-reactivity with other Salmonella species, the test cannot distinguish between a current infection and a previous infection or vaccination against typhoid. However the test is applied for enteric fever that include typhoid and paratyphoid. A person infected with S. Typhi will produce in his serum the O and H antibodies which can be tested for by using the antigen suspensions of O somatic 1, 9, 12, VI and H flagellar antigen. In acute infection, 'O' antibody 9 of IgM type appears first, rising progressively, later falling of antibody. The IgG type antibodies appear slightly later but persist longer. The Widal testing method has its limitations, as Many individuals possess a low titer agglutinins that reacts with salmonella antigens. Hence a rising titer gives more significance than a single test. While the Widal test has played a major role in the diagnosis of typhoid fever in the past, technical developments have revealed several pitfalls in its use and interpretation of its result. Clinically, it is obvious that a single Widal test in an unvaccinated or unexposed patient may have some diagnostic relevance. However, the result of such a single test has no diagnostic significance in an endemic region; in part due to difficulty in establishing a steady-state or baseline titer of Widal agglutination, which limits the usefulness of the test as a reliable diagnostic indicator of the disease process. However in many Hospitals settings a single testing is performed as the Physicians were reluctant send a paired sample with the response to the antibiotics. In endemic countries like India, sera of a proportion of healthy individuals contain antibodies capable of reacting to a variable titre in Widal test due to previous stimuli or as under the criteria of anamnestic reactions Therefore, baseline titres for anti-O and anti-H for Salmonella typhi and anti-H for Salmonella paratyphoid A, and B were to evaluated and established and Widal test results were reported accordingly taking the consideration of base line titers.

READING THE RESULTS

1 The result of positive control should be read before reading the test result. The satisfactory result of positive control indicates that the reagents are working well.

2. Factors other than reagents, which might affect the performance of the test, include cleanliness of glassware, meticulous follow up of the procedure.

3. Positive result only indicates salmonella infection. A rise in titer after a week should be checked to confirm the infection.

4. Agglutination with O Antigen with titer less than 1:80 is not significant.

Read the results under high intensity of light. Regardless of the degree of reactivity and test results showing slight but definite agglutination is reported as reactive or positive. Complete absence of agglutination and a clear suspension indicates negative result.

B. Semi quantitative Analysis: Agglutination may be observed in normal serum up to a titre of 1:80. A titre of 1:80 (Slide) or more is considered significant and a rise in titre after a few days will confirm the diagnosis. An individual who been previously immunized or inoculated with vaccine or have a history of enteric illness the Widal test limits the interpretative criteria. To confirm the infection a rise in titre after a few days should be checked. A moderate rise in titer of all three (H) agglutinations simultaneously against all 'H' suggestive of TAB vaccination. However in the current contest a very few take vaccination in India for Enteric fever, except travellers and people who conscious higher standards of health and Hygiene. Many rapid card tests miss the Diagnosis of

Paratyphoid A and B infections as the respective antigens are not

configured in the system. YET WE HAVE NO RAPID, SPECIFIC, SENSITIVE TEST FOR DIAGNOSIS OF TYPHOID FEVER AVAILABLE IN MAJORITY OF DEVELOPING COUNTRIES.

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