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 KERALAThe gold standard in diagnosis of Enteric fever remains when the pathogencan be recovered from the blood during the first 7-10days of illness. TheWidal test continues to be a popular test done in many Developingcountries as presumptive diagnosis of Typhoid fever. Although the test isno longer commonly performed in the developed countries, it is still inuse in many developing countries where enteric fever is endemic withlimited resources; however we require the use of rapid, affordable testingalternatives. For diagnosing a case of enteric fever, Widal test is thesecond most widely used test after blood culture. Widal test using antigensuspensions appropriate to the diagnosis of the prevalent enteric feveragents has been used either to compare paired sera or to test a singleserum taken on admission to see significant antibody levels. In endemicareas, such as India the bacterial culture facilities are often unavailable orlimited to teaching Hospitals and accredited laboratories. The bloodculturing continues to be unpredictable proving sterile with uncontrolled,empirical use of Antibiotics in particular Cephalosporin group ofAntibiotics. Howeverthe Widal test continues to be the most simple, overutilized, specific diagnostic?Investigation tool available in the localLaboratories in developing countries. It is named after GEORGESFERDINAND WIDAL, who introduced it; the method relies on a reaction ina test tube or on a slide between antibodies present in the infectedpersons blood sample and specific antigens of S. typhi, which producesclumping (agglutination) that is visible to the naked eye. While themethod is easy to perform, concerns remain about the reliability of theWidal test and studies of the assay of sensitivity and other measures of
reliability have been doubtful. Besides cross-reactivity with otherSalmonella species, the test cannot distinguish between a current infectionand a previous infection or vaccination against typhoid. However the testis applied for enteric fever that include typhoid and paratyphoid. A personinfected with S. Typhi will produce in his serum the O and H antibodieswhich 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 IgMtype appears first, rising progressively, later falling of antibody. The IgGtype antibodies appear slightly later but persist longer. The Widal testingmethod has its limitations, as Many individuals possess a low titeragglutinins that reacts with salmonella antigens. Hence a rising titer givesmore significance than a single test. While the Widal test has played amajor role in the diagnosis of typhoid fever in the past, technicaldevelopments have revealed several pitfalls in its use and interpretation ofits result. Clinically, it is obvious that a single Widal test in an unvaccinatedor unexposed patient may have some diagnostic relevance. However, theresult of such a single test has no diagnostic significance in an endemicregion; in part due to difficulty in establishing a steady-state or baselinetiter of Widal agglutination, which limits the usefulness of the test as areliable diagnostic indicator of the disease process. However in manyHospitals settings a single testing is performed as the Physicians werereluctant send a paired sample with the response to the antibiotics. Inendemic countries like India, sera of a proportion of healthy individualscontain antibodies capable of reacting to a variable titre in Widal test dueto previous stimuli or as under the criteria of anamnestic reactionsTherefore, baseline titres for anti-O and anti-H for Salmonella typhi andanti-H for Salmonella paratyphoid A, and B were to evaluated andestablished and Widal test results were reported accordingly taking theconsideration of base line titers.
READING THE RESULTS 1 The result of positive control should be read before reading the testresult. The satisfactory result of positive control indicates that thereagents are working well.2. Factors other than reagents, which might affect the performance of thetest, include cleanliness of glassware, meticulous follow up of theprocedure.3. Positive result only indicates salmonella infection. A rise in titer after aweek 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 ofreactivity and test results showing slight but definite agglutination isreported as reactive or positive. Complete absence of agglutination and aclear suspension indicates negative result.B. Semi quantitative Analysis: Agglutination may be observed innormal serum up to a titre of 1:80. A titre of 1:80 (Slide) or more isconsidered significant and a rise in titre after a few days will confirm thediagnosis. An individual who been previously immunized or inoculatedwith vaccine or have a history of enteric illness the Widal test limits theinterpretative criteria. To confirm the infection a rise in titre after a fewdays 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 forEnteric fever, except travellers and people who conscious higher standardsof health and Hygiene.Many rapid card tests miss the Diagnosis ofParatyphoid A and B infectionsas the respective antigens are not
configured in the system. YET WE HAVE NO RAPID, SPECIFIC, SENSITIVETEST FOR DIAGNOSIS OF TYPHOID FEVER AVAILABLE IN MAJORITY OFDEVELOPING COUNTRIES.Emaildoctortvrao@gmail.com