‫‪1‬‬
‫‪Significance and value of the Widal test in the diagnosis of‬‬
‫‪typhoid fever in an rural area in najaf city.‬‬
‫‪Israa Kitab Al- Yasiri‬‬
‫‪College of Dentistry, Kufa University.‬‬
‫الخالصة‪:‬‬
‫لدراسة مدى مالئمة اختبار ويدال المفرد وللكشف عن مددى عاالةدة اد ا االختبدار عد تشدية‬
‫ممد‬
‫التايفوئةد‪ .‬ا ه الدراسة تضمنت كل األعمار وقسمت إل ثالث مجامةع (‪ )I‬مئة متبرع من األصداا‬
‫كمجموعة سةطرة (‪ ) II‬مئة عةنة دم لغرض الزرع البكتةري مدن مرىد مبدا ةن امد التايفوئةدد‬
‫(‪ )III‬ألددف وأر اددة مئددة وخمسددوظ مددريال يت ددروظ عالمددا سددريري لامد التايفوئةددد ‪ .‬مجموعددة‬
‫السددةطرة مددن المتبددرعةن األصدداا تددا عاب د ا واسددطة اختبددار الددتال ظ لبكتريددا السددالمو ةال النددوع‬
‫المبل تايف‬
‫للمستضد ‪ O‬و‪ H‬كد ل تدا عمدل الدزرع البكتةدري للاةندا ‪ .‬عد اد ه الدراسدة كا دت‬
‫مساسةة عا‬
‫الويدال ‪ %75.5‬أما مقدار تيببةة االختبار كا ت ‪ %83‬ةنما كا ت تائج مساسةة‬
‫الزرع البكتةري ‪ %56‬أمدا تيببدةة الدزرع البكتةدري ‪ .%100‬مدن اد ا سدتنتج أظ اختبدار الويددال‬
‫أكثددر مساسددةة مددن الددزرع البكتةددري ةنمددا الددزرع البكتةددري أكثددر تيببددةة ع د تشددية‬
‫التايفوئةدددد‪ .‬أمدددا النسدددبة لفاددد‬
‫للتشدددية‬
‫مم د‬
‫الدددتال ظ للمستضدددد ‪ O‬و‪ H‬عددداظ التيفةدددف ‪ 1/160‬أكثدددر مانويدددة‬
‫‪.‬و ّ‬
‫إظ اختبدددار الويددددال رخدددة‬
‫سددد ل‪ ،‬وغةدددر مددد ي سدددبةا‪ .‬واظ لفاددد‬
‫الويددددال قةمدددة‬
‫تشيةبةة عندما يكوظ الزرع البكتةري للد ّم غةر متوعر أَو عمل ‪.‬‬
‫‪Abstract:‬‬
‫‪To study the reliability of a single Widal test and to find out the diagnostic‬‬
‫‪Significance of this test in the diagnosis of typhoid fever. This study was‬‬
‫‪included all ages and was divided into three groups: (i) 100 healthy blood‬‬
‫‪donor controls group, (ii) 100 patients blood sample for culture for‬‬
‫‪Salmonella enterica serotype Typhi and (iii) 1450 patients with a clinical‬‬
‫‪diagnosis of typhoid fever. Blood donor controls were screened with a slide‬‬
‫‪agglutination test for the Salmonella enterica serotype Typhi O and H‬‬
2
antigens, and blood culture. In this study Widal test had a sensitivity of
75.9% and a specificity of 83%. While blood culture for Salmonella enterica
serotypes Typhi had a sensitivity of 56% and a specificity of 100%. We
concluded that the Widal test was more sensitive than blood culture while
blood culture was more specific than Widal test. And O and H agglutinin
titres of 1/160 are of diagnostic significance. The Widal test is easy,
inexpensive, and relatively noninvasive. It can be of diagnostic value when
blood cultures are not available or practical.
Introduction:
Typhoid fever is a life threatening systemic infection occurring in lesserdeveloped areas of the world and continues to be a major public health
problem. There are at least 16 million new cases of typhoid globally (1). The
annual incidence of typhoid fever has been reported as more than 13 million
cases in Asia and causing more than six lakhs deaths worldwide annually(2).
Typhoid fever was introduced by typhoid cases in the households and
facilitated by poor handwashing hygiene and sharing of food from the same
plate. (3) The association of poor hand-washing hygiene and typhoid fever
was shown in Indonesia and India. (4, 5).
The clinical picture of typhoid fever is nonspecific; confirmed diagnosis
through blood or bone-marrow culture requires expensive and laborintensive isolation and identification of the organism, which may take up to
seven days. A cheap and rapid alternative laboratory test is desirable,
especially for developing country settings where typhoid fever is a major
public health burden. Various agglutination tests have been developed (6) of
which the Widal method is the oldest and remains the most widely used.
The test was first introduced by F. Widal in 1896 (6) and is based on a
macroscopically visible serum – mediated agglutination reaction between S.
3
typhi somatic lipopolysacharide O antigens (TO) and flagellar H antigens
(TH). Although a definitive diagnosis can be made by isolation of
Salmonella typhi from blood or bone marrow.(7,8) Serological diagnosis
relies classically on the demonstration of a rising titre of antibodies in paired
samples at an interval of 10–14 days.(9)
In typhoid fever, however, a four fold rise after 2 weeks in not always
demonstrable, even in blood culture confirmed cases. This situation may
occur because the acute phase sample was obtained late in the natural history
of the disease, because of high levels of background antibodies in an
endemic region, or because in some individuals the antibody response in
blunted by the early administration of an antibiotic. (10) For practical
purpose a treatment decision must be made on the basis of results obtained
with a single acute phase sample. The cut-off for a positive Widal, chosen in
a particular community depends on the background level of typhoid fever
(i.e., the prior probability) and the level of typhoid vaccination, which may
vary with time. (11) In endemic areas, the bacterial culture facilities are
often unavailable or it is not always available and, when it is, it takes 2 to 3
days. As a result, diagnosis may be delayed or overlooked and patients
without typhoid fever may receive unnecessary and inappropriate
antimicrobial treatment. For this reason, in developing countries typhoid
rapid antibody tests can facilitate diagnosis and disease management. (12,13)
Present study tried to evaluate the value of a single acute phase Widal test
for the diagnosis of typhoid fever in an rural area in najaf city.
Materials and methods:
Study group:
This study performed on person who were admitted to Al –Sajad hospital, in
the period from 1-1-2010 to 1-1- 2011.
4
The study were included all ages and were divided into three groups:
(i) 100 healthy blood donor controls, (ii) 100 patient blood sample for
culture for Salmonella enterica serotype Typhi and (iii) 1450 patients with a
clinical diagnosis of typhoid fever.
Isolation of bacteria:
Salmonella enterica serotype Typhi was isolated from blood cultures.
Cultures were plated on eosin-methylene blue, salmonella-shigella agar.
Lactose-nonfermenting colonies were isolated from these culture plates, and
tests using various agents were performed. Serotype Typhi strains were
identified as H2S positive, motile, urease negative, non-gas forming. (9, 10).
Widal test:
The Widal test was performed with standardized kits. Serum samples of
patients were screened with a slide agglutination test which measures
agglutinating antibodies against the lipopolysaccharide ‘O’ and protein
flagellar ‘H’ antigens of S. typhi and Para typhi A and B. Serial dilution of
sera starting at a dilution of 1:40 were made with 0.9% saline and examined
for visible agglutination. Appropriate positive and negative sera were
included.
Statistical analysis:
All the statistical analysis were done by using Pentium-4 computer
through the SPSS program (version-14) and the performance characteristics
(validity) of a test or criteria include among others: sensitivity and
specificity(14).
Formulas used in calculation
Sensitivity = Number of true positives \ Number of diseased people
Specificity = Number of true negatives \ Number of non-diseased people
Also Chi-square test was used to accept or reject the statistical hypotheses.
5
Results:
Among 1450 blood samples of individuals tested 1100(75.8%) were
positive for agglutinins of Salmonella serotypes Typhi. (Table -1).
Table 1: Results of Widal test.
Widal status
frequency
percentage
Total participants
1450
100%
Positive for agglutinin ≥ 1 in 40
1100
75.8%
Negative for agglutinin ˂1 in 40
350
24.2%
Blood culture was positive for Salmonella enterica serotype Typhi in 56
out of 100 patients (group I), whereas the entire 100 individual in group II
(control) were sterile on blood culture for Salmonella enterica serotype
Typhi. Amongst all the 100 patients in Group I, 56 were having positive
blood culture giving a sensitivity of 56% and specificity of 100% and there
is highly significant differences between patient and control in culture
results P = 0.000. (table 2 ).
Table 2 : Comparison of Blood culture in patients and healthy control.
patient
control
P –value
Positive result
56
0
X ²= 77.778
Negative result
44
100
P = 0.000
Total
100
100
test
Sensitivity =56%
6
Specificity=100%
Widal test was positive in 1100 patients of group I while only 17
individual in group II (control) were widal positive. Amongst all the 1450
patients in Group I, 1100were having positive Widal test giving a sensitivity
of 75.9 % and specificity of 83% and there is highly significant differences
between patient and control in widal results P = 0.000 (table 3).
Table 3 : Comparison of widal test in patients and healthy control.
test
patient
control
p- value
Positive result
1100
17
X ²=161.001
Negative result
350
83
P = 0.000
Total
1450
100
Sensitivity =75.9%
Specificity =83%
In this study, 570(51.8%) patient with typhoid fever had detectable O
antibodies at a cut-off titre of 1:80 and 660(60%) patient had detectable H
antibodies at a cut-off titre of 1:80.While 165(15%) patient with typhoid
fever had detectable O antibodies at a cut-off titre of 1:160 and 130 (11.8%)
patient had detectable H antibodies at a cut-off titer of 1:160. A substantial
O/H agglutinin titre of 1/320 was observed in 9-10.9% cases respectively
while only 1.2–1.6 % of patients respectively had substantial H/O agglutinin
titre of 1/640. (Table - 4).
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Table 4: Agglutinin level against TO, TH in 1100 proven cases typhoid
fever.
Widal Titre
1.40
1.80
1.160
1.320
1.640
Anti-O
antigen
Number 978
570
165
100
14
88.7
51.8
15
9
1.2
Anti-H
antigen
Number 1021
660
130
120
18
60
11.8
10.9
1.6
%
%
92.8
X ² =10.05
P ≤ 0.039
Discussion:
Typhoid fever is a systemic illness with a significant morbidity and
mortality in developing countries. Poor sanitation, overcrowding, low
standard of living, lack of medical facilities, and indiscriminate use of
antibiotics lead to endemicity of typhoid fever and multi-resistant strains of
Salmonella typhi in developing countries(15,16). Blood culture has remained
the gold standard test in diagnosis of typhoid fever, but its utility in early
diagnosis is limited in early phase of illness thereby making the isolation of
the organism difficult. Also many patients have already taken antibiotics
before being seen by a physician that give the negative result for culture.
Widal test has been used for over a century in developing countries for
diagnosing typhoid fever .the present study was supported by the study(17)
of a group of workers who reported that in developing countries with a high
incidence of typhoid fever co agglutination test is more reliable than culture.
8
But there was some limitation because previous typhoid vaccination may
contribute to elevated agglutinins in the non infected population. Present
study observed that a high titre of antibodies to somatic O antigen (1:160
and 1:320) is consistent with acute typhoid and high titers (1:320) are even
more suggestive of this condition. Antibodies to flagellar O antigen may be
found in higher titres than H. P ≤ 0.039 as shown in table 4. This study was
contrast to study introduced by Herrera and Valenzuela who found that
Antibodies to flagellar H antigen may be found in higher titres than O. (18)
and the Present study was supported by the study (19) of a group of workers
who reported that the level of ‘O’ agglutinins was found to be more helpful
than the level of ‘H’ antigens.
This result showed that a noteworthy O agglutinin titre of 1/320 in 9% of
typhoid cases and in only 1.2% of patients considerable O agglutinin titre of
1/640. This study was agreement with number of studies (1, 11).who
reported highly specific and positive predictive value in 1:160 makes the
Widal test acceptable as a diagnostic tool. Seroprevalence studies in healthy
person can help to validate the use of a particular serological cut-off point.
Conclusion:
This study revealed that in endemic areas the Widal test is still of
significant diagnostic value provided judicious interpretation of the test is
made against a background of pertinent information, especially data which
relate to agglutinin levels in normal individuals in the region. We also point
out that in endemic areas a single Widal test can be of diagnostic value in the
early stage of disease and thus help in reducing morbidity and mortality
from typhoid. The Widal test is easy, inexpensive, and relatively noninvasive. It can be of diagnostic value when blood cultures are not available
or practical.
9
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