WIDAL TEST - WHY WE STILL DO IT ?

1. 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

2. 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.

3. 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 infectionsas the respective antigens are not

4. 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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