Widal Agglutination Research Articles

Comparative evaluation of various tests for diagnosis of concurrent malaria and typhoid Fever in a tertiary care hospital of northern India.

Malaria and Typhoid are two major infectious diseases, still prevalent in most of the tropical countries including India. Millions of individuals residing in these endemic cases contact these diseases either concurrently or as acute infection superimposed on a chronic one. Diagnosis and comparative evaluation of various tests for diagnosis of Typhoid- Malaria co-infection in patients suffering from febrile illness. Around 800 patients of both Out Patient Department (OPD) and In Patient Department (IPD) were referred to microbiology lab for Widal test/ Typhi dot IgG/IgM and Malaria card test between July 2012- September 2012. Patients found to be suffering from co-infection were further confirmed for typhoid by blood culture. Those patients who were found sterile on blood culture were further confirmed by stool culture. Patients positive by Malaria card test (either antibody or antigen or both) were confirmed by peripheral blood smear examination for malaria parasite by both thick and thin smear examination. 68 (8.5%) patients were found to be suffering from co- infection by the above tests. Blood culture revealed 15 (22%) bacterial pathogens in the widal positive patients out of which 6(8.8%) were Salmonella Typhi and 3 (4.41%) were Salmonella Paratyphi A. Stool culture revealed 8 (11.7%) S.Typhi and 5 (7.35%) S. Paratyphi A cases. Out of 68 patients positive by Malaria card test, only 36 (52.94%) showed Malaria parasite in peripheral blood smear also. Thus the no. of confirmed cases of co-infection was found to be only 1.6%. The interpretation of Widal test and Malaria card test, when diagnosing concurrent malaria and typhoid fever, must therefore be done with a lot of caution. Negative or positive Widal agglutination test is neither definitive nor completely informative. Similarly erroneous interpretation of Malaria card test (especially Antibody detection card test) result may lead to prolonged treatment and economic burden on patient.

English

BACKGROUND: Typhoid fever, caused by Salmonella Typhi, is endemic in the Indian sub-continent including Bangladesh, South-east and Far-east Asia, Africa and South Central America. The disease can occur in all age group with highest incidence among children. A simple, reliable, rapid and early diagnostic test has been a long felt need of the clinicians. Blood culture is regarded as the gold standard for diagnosis. However, this requires laboratory equipment and technical training that are beyond the means of most primary health care facilities in the developing countries. To fulfill the purpose the present study was carried out in the Department of Microbiology, Era's Lucknow Medical College and Hospital for the period from Oct 2012 to Mar 2013. MATERIALS AND METHODS: 300 blood samples, collected aseptically from patients clinically diagnosed of Typhoid fever, were evaluated by blood culture, Tube and Slide Widal test RESULTS: This study included 300 cases having clinical suspicion of typhoid fever. Subjects were investigated by blood culture, Tube & Slide Widal agglutination tests. Among them, 42(14%) were subsequently confirmed by blood culture for S. Typhi, 123(41%) and 150(50%) cases were positive as having significant titre of Slide and Tube Widal agglutination tests respectively. Thus, in comparison to the gold standard test i:e blood culture, Tube and Slide Widal test were better and consumed less time. Comparing Slide and Tube Widal test, Tube is better. CONCLUSION: Tube& Slide Widal agglutination test is found to be better and could be applied as a good alternate in resource poor nation. Further, it is simple to perform, reliable when compared to blood culture test, and rapid, with results being available in 18 hrs when compared to 48 hours for blood culture.

English

AIM AND OBJECTIVE: The interpretation of the Widal test depends upon the baseline titre among healthy individuals in a particular geographical area. This study was undertaken to determine the baseline Widal titre in apparently healthy individuals in, Hadoti region, Rajasthan. MATERIALS AND METHODS: Blood samples were collected from healthy blood donors (n= 200) who attended blood bank of this institution from May 2012 to August 2012. The Widal tube agglutination test was carried out. 0.5 ml of two fold serially diluted patients' sera (dilutions from 1:20 to 1:160) in 0.9% normal saline was tested by adding an equal amount of antigen. RESULTS: Of the 200 serum samples which were tested, 108 serum samples were positive for agglutinins against Salmonella serotypes (≥ 1:20) and 92 serum samples were negative for agglutinins. Among 54 samples with an anti-O titer (≥ 1:20) , 39 samples had titres of 1:40. Among the 63 samples demonstrating anti-H titres of ≥ 1:20 to salmonella serotype, 48 had a titer of 1:40. For salmonella Paratyphi A and B, anti-H titres of 1:20 were found in 3% and 1.5%, respectively, of all samples tested. CONCLUSION: We recommended that the significant titre of the 'H' agglutinin and the 'O' agglutinin of Salmonella Typhi is ≥ 1: 80. While the significant titre of the 'H' agglutinins of Salmonella Paratyphi A and Salmonella Paratyphi B is ≥ 1: 40.

Determination of Baseline Widal Titres Amongst Apparently Healthy Blood Donors in Ahmednagar, Maharashtra, India

Enteric fever is endemic in all parts of India. The Widal agglutination test is widely used for its diagnosis. But the interpretation of Widal test depends upon the baseline titre which is prevalent amongst healthy individuals in a particular geographical area. Present study was undertaken to establish the normal baseline titre in apparently healthy blood donors and also to determine cutoff values for the Widal test. One hundred and three (103) sera were tested by the Widal tube agglutination test from January 2012 to February 2013. Eighty four (81.55%) sera were positive for agglutinins (titre ≥ 1:20) and the remaining 19 were negative. 31.64% sera were positive for agglutinins of 'O' antigen of Salmonella typhi (TO) at a titre of 1:40, 33.87% sera were positive for 'H' antigen of Salmonella typhi (TH) at a titre of 1:40 and 38.46% and 36.84% sera were positive for 'H' antigen of Salmonella paratyphi A (AH) and Salmonella paratyphi B (BH) respectively, both at a titre of 1:80. Therefore, the baseline titre for TO and TH was noted to be 1:40 and that for AH and BH was noted to be 1:80 and therefore, the cutoff level for TO and TH was ≥ 1:80 and that for AH and BH was ≥ 1:160.

The Baseline Widal Titre Among the Healthy Individuals of the Hilly Areas in the Garhwal Region of Uttarakhand, India

Typhoid fever is endemic in all parts of India and the Widal test is widely used for its diagnosis. In the endemic areas, the healthy people may contain antibodies which are capable of reacting upto a variable titre in the Widal test, due to a past exposure, TAB vaccination and cross reacting antigens. Therefore it varies widely from place to place and is referred to as the baseline titre of that area. The aim of this study was to determine the average baseline titre of the apparently healthy population in the Garhwal region of Uttarakhand, India. Blood samples were collected from healthy volunteers over the period from February 2011 to January 2012 and they were analyzed for the presence of the Salmonella antibodies by carrying out the Widal tube agglutination test. Among the 2164 serum specimens which were tested, 922 (42.6%) sera were found to be positive for the Widal test and 1242 were negative. The most frequently recorded titre of the reactive sera was 1:40 for the anti-O antibodies and it was 1:80 for the anti-H antibodies and this was the baseline titre for this region. Based on the above results of our study, it has been recommended that the cut-off titre of 1:80 for the anti-O antibodies and of 1:160 for the anti-H antibodies may be considered as diagnostic for enteric fever in the Garhwal region of Uttarakhand, India.

Rate of Malaria-Typhoid co-infection among Pregnant women attending Antenatal Clinics in Anambra State South- East Nigeria.

Background: Malaria and typhoid fever are both endemic in the tropics and pregnant women constitute one of the high risk groups. Objective: To determine the rate of malariatyphoid co-infection in pregnant women attending antenatal clinics in hospitals in Anambra State, South –East Nigeria. Methodology: A cross sectional study of 700 volunteer pregnant women recruited during routine antenatal clinics in five major public and private hospitals in Anambra State, South- East Nigeria was conducted. Malaria infection was determined by qualitative immunodiagnostic assay and confirmed by microscopic examination of thick and thin Giemsa stained slides. Typhoid infection was determined by Widal agglutination method and confirmed by stool culture. Results: Out of 700 pregnant women studied 512 (73.1%) were malaria parasite positive and out of this number 236 (46%) had significantly positive Widal reaction. Out of 100 stool samples cultured 20 (20%) were positive for Salmonella. This shows that the rate of Malaria –typhoid co-infection was 46% by Widal agglutination method and 20% by stool sample method. Conclusion: The study showed that malaria was complicated by typhoid fever in pregnancy in at least 20% of the cases and this has a far reaching effect on adverse pregnancy outcome. This has immense public health implication.

Modifications Influencing Widal Test Reactivity in a Novel Microplate Assay

Reliability of the Widal tube agglutination test has been the subject of many controversies over the years. This study was performed to assess the effect of certain modifications on the performance of Widal test in a novel microplate assay. Sera from 37 patients (21 males; 16 females) (mean age 28 +/- 7 years) were tested in the Immunology Unit at King Khalid University Hospital, Riyadh. Among them were 26 patients with suspected typhoid fever and 11 had bacteriologically confirmed diagnosis of Salmonella infection. The modifications included either the use of 0.5% bovine serum albumin (BSA), absorption of sera with sheep red blood cells (SRBC) or heat inactivation of sera. Compared with Widal tube agglutination test, microplate assay with SRBC absorption of the sera from patients with suspected typhoid fever was not only associated with enhancement of detection titers for both H (p < or = 0.001) and O (p < or = 0.005) Salmonella agglutinins but also the percentage of reactivity. The presence of BSA augmented detection titers for Salmonella H agglutinins (p < or = 0.02) only. Heat inactivation of sera however was found to be associated with reduction in the detectable titers for both H (p < or = 0.03) and O (p < or = 0.01) agglutinins. Increased titers of Salmonella agglutinins were also evident in 11 patients with confirmed diagnosis of Salmonella infection. The novel microplate agglutination assay using the SRBC absorption was associated with enhancement in Widal test reactivity and appears to be a useful alternative for the diagnosis of Salmonella infection.

A retrospective study of community-acquired Salmonella infections in patients attending public hospitals in Lagos, Nigeria

A retrospective cohort study on Salmonella-associated diseases (SADs) was conducted in 14 public hospitals across Lagos State, Nigeria, between 1999 and 2008. Medical records of clinically diagnosed patients with confirmed Salmonella infections were reviewed for the 10-year period. Laboratory diagnosis of typhoid fever cases in all the hospitals were first based on Widal agglutination tests then followed by culture, while non-typhoidal Salmonella infections were based on culture technique. A total of 85,187 confirmed cases of SADs were found, of which 880 deaths were recorded (case-fatality rate = 1.03% / 10 years). The mean incidence of SADs in Lagos State for the 10-year period was estimated at 45 cases per 100,000 persons/year, while that of typhoid fever alone was 16 cases per 100,000 persons/year. During the studied period, the number of deaths due to typhoid fever was significantly (P < 0.05) higher than deaths due to gastroenteritis except in 2003 and 2004. Risk associated with typhoidal deaths was 4 to 11 times greater when compared to gastroenteritis deaths between 2000 and 2002. Salmonella-associated diseases were most prevalent in adults 21 to 30 years of age (49.49%). Cases of patients with invasive Salmonella-associated gastroenteritis were observed mainly in children under five years of age. The current surveillance data indicated high incidence of SADs in areas exposed to environmental contaminations. This study revealed that infections caused by Salmonella enterica serovars are endemic in our environment thus poses a serious threat to public health. Constant public health education is essential to avert undue epidemics.

English

The object of this study is to observe the&nbsp;in vivo&nbsp;effect of cyclo-oxygenase-2 (Cox-2) inhibitors on the humoral response after immunization of rabbits with&nbsp;Salmonella typhi&nbsp;antigen. Albino rabbits of either sex were divided into five groups of six animals each and were administered aspirin (100 mg/kg, (BD), p.o), celecoxib (30 mg/kg O.D, p.o), indomethacin (12.5 mg/kg BD, p.o) and etoricoxib (17 mg/kg O.D, p.o) for seven days starting one day prior to immunization with&nbsp;S. typhi&nbsp;antigen (0.5 ml in each thighs), respectively. The antibody titres were measured weekly for a month using Widal agglutination test. The antibody titres in the first week were augmented in all the groups. The response was more marked in treated group as compared to control group. Later on antibody titre fell markedly in the treated groups. Selective Cox-2 inhibitors administration caused higher antibody suppression in comparison to non-selective Cox inhibitors treatment. These findings support that NSAIDs and the new Cox-2-selectivedrugs have an unsuspected target, the B cell, and attenuate&nbsp;antibody production. &nbsp; Key words:&nbsp;Non-steroidal anti-inflammatory drugs&nbsp;(NSAIDS), cost, immunomodulators, antibody production.

Evaluation of the Widal tube agglutination test for the diagnosis of typhoid fever among children admitted to a rural hdospital in Tanzania and a comparison with previous studies

BackgroundThe diagnosis of typhoid fever is confirmed by culture of Salmonella enterica serotype Typhi (S. typhi). However, a more rapid, simpler, and cheaper diagnostic method would be very useful especially in developing countries. The Widal test is widely used in Africa but little information exists about its reliability.MethodsWe assessed the performance of the Widal tube agglutination test among febrile hospitalized Tanzanian children. We calculated the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of various anti-TH and -TO titers using culture-confirmed typhoid fever cases as the "true positives" and all other febrile children with blood culture negative for S. typhi as the "true negatives."ResultsWe found that 16 (1%) of 1,680 children had culture-proven typhoid fever. A single anti-TH titer of 1:80 and higher was the optimal indicator of typhoid fever. This had a sensitivity of 75%, specificity of 98%, NPV of 100%, but PPV was only 26%. We compared our main findings with those from previous studies.ConclusionAmong febrile hospitalized Tanzanian children with a low prevalence of typhoid fever, a Widal titer of ≥ 1:80 performed well in terms of sensitivity, specificity, and NPV. However a test with improved PPV that is similarly easy to apply and cost-efficient is desirable.

Distribution of antibody titer against Salmonella enterica among healthy individuals in nepal

BackgroundEnteric fever is an endemic problem in Nepal and Widal agglutination test is widely used for its diagnosis but a normal baseline titer in healthy population and cutoff values have not been established.MethodsWe measured average baseline antibody titers against "O" and "H" antigens of Salmonella enterica serotype Typhi and "H" antigens of serotypes Paratyphi A and Paratyphi B among apparently healthy blood donors in Nepal. The antibody titers were measured using Standard Widal Confirmatory Quantitative Tube test.ResultsAmong the 100 blood samples collected from healthy volunteers, 62 individuals had significant antibody titers (≥ 1:20) against one of the four antigens against S. enterica. Among 54 samples with an anti-O titer against serotype Typhi, 15 and 36 samples had titers of ≥ 1:60 and ≥ 1:40, respectively. A significant proportion (12% of all) had anti-O titer of ≥ 1:80. Similarly, among the 59 samples demonstrating anti-H titers of ≥ 1:20 to S. enterica serotype Typhi, 29 had a titer of ≥ 1:80 and 12 had 1:160. For S. enterica serotypes Paratyphi A and B, anti-H titers of ≥ 1:20 were found only in 12% and 3%, respectively, of all samples tested.ConclusionWhen a single Widal agglutination titer is used for the diagnosis of enteric fever, it will be more appropriate to change the currently used cutoff levels against S. enterica serotype Typhi to > 1:80 for anti-O and > 1:160 for anti-H titers for Nepal.

The comparison of cultures, widal agglutination test and polymerase chain reaction as a diagnostic tool in typhoid fever

Abstract Typhoid fever caused by Salmonella typhi, paratyphi A and B, is an important cause of morbidity and mortality in many developing countries. A rapid and sensitive method for the detection of S. typhi is essential for early diagnosis of typhoid fever and effective therapy. In this study 45 febrile patients who were suspected to have enteric fever were enrolled, and the results of blood cultures, widal agglutination tests and Polymerase Chain Reaction in these cases were evaluated. Group I consisted of 11 patients with diseases other than salmonella infections, group II represented 6 patients with positive cultures, and group III represented 28 patients with negative blood cultures negative but who were clinically suspected cases that had a medical history of using variable antimicrobial agents. Two positive PCR results were present; one of them was in culture positive group (16,6%) and the other was in culture negative group (3,5%). In our study widal agglutination tests and cultures were found not to be helpful in differential dignosis. Although PCR based detection of S. typhi is reported to be a sensitive and specific test for the diagnosis of enteric fever, in our study the benefit of this method in the diagnosis of especially patients who were treated with antimicrobial therapy was not clearly determined. Other methods to increase sensitiviy and specificity to levels such as those of real time PCR should be developed and large-scaled studies should be done in endemic and non-epidemic regions.

Interpreting widal agglutination test in diagnosis of typoid fever

Interpreting widal agglutination test in diagnosis of typoid fever

The Sensitivity Of Diazo Test In The Diagnosis Of Enteric Fevers

To ascertain the sensitivity of Diazo (chemical) test in comparison to the Widal (serological) test in the diagnosis of enteric fevers, blood specimens from101 patients suspected of having enteric fevers were collected. 54.5% (55) of the patients were significantly seropositive. Fifteen urine specimens from these 55 seropositive patients were positive for Diazo tests, giving a sensitivity of about 27%. Salmonella typhi was the predominant serotype causing typhoid/paratyphoid fevers, followed by S. paratypi A; S. paratyphi C and S. paratyphi B respectively. Although Diazo test does not appear to be reliable, it could still be useful alongside with Widal agglutination test in endemic rural or urban areas where electricity and facilities are absent or inadequate for routine laboratory investigations. African Journal of Clinical and Experimental Microbiology Vol. 9 (3) 2008: pp. 115-118

Typhoid is over-reported in Embu and Nairobi, Kenya

The paper looks at the usefulness of the Widal agglutination test in the context of variable normal antibody titres in two different populations in Kenya, and in comparison to the blood culture method of diagnosis. It presents a prospective case-control study. We examined 846 blood cultures and an equal number of serum samples, and 782 stools from adults who presented at two study sites; Kenyatta National Hospital and one hospital and 3 clinics in Embu District, with symptoms similar to typhoid. Examined also were 360 serum samples and stools from adults who were apparently healthy (controls) who sought routine medical examination at the study sites. From blood cultures, isolation rates for typhoid for Embu (3% ) and Nairobi (2.2%) were not significantly different (p>0.01). In addition the control population from the two study sites did not show any significant background O antibody titre levels characteristic of typhoid endemic areas. All the 7 commonly available Widal test kits including Murex, Europath, Biotech, Humatex, Biosystems, Microsystems and Typhex, that were evaluated for efficacy were equally specific in diagnosis of typhoid by Widal agglutination methods. However, there were minor differences in the sensitivities of the kits. The Widal test method gave a lower sensitivity (81.3%) than specificity (93%) when compared to the culture of blood for diagnosis of typhoid. Going by the reports of typhoid outbreaks in Embu and Nairobi (ca. 20-25% reported prevalence) we conclude that there has been over-reporting probably due to poor methodologies of performing the Widal test. We recommend adequate clinical examination in suspected cases of typhoid in addition to proper Widal in order to improve typhoid diagnosis. Newer improved methods that are more specific and sensitive than the Widal test need to be evaluated in improving laboratory diagnosis of typhoid.

Blood Leucocyte Count Patterns in Relation to Salmonella Agglutinins among Patients with Salmonellosis in Ibadan, Oyo State, Nigeria

One hundred blood samples of clinically diagnosed tyhoid fever patients attending University College Teaching Hospital Ibadan were subjected to Widal agglutination test and blood leucocytes count. Mean WBC values of 5354 and 6059 per ml were obtained at a tire of 1/160 for ‘O\' and ‘H\' agglutinins, while 6157 and 5286 per ml for ‘O\' and ‘H\' agglutinins at a tire of 1/320 were recorded respectively. Similar patterns of normal response were also obtained in the differential leucocytes count. The mean values of total leucocytes, neutrophils and lymphocytes of the patients analyzed at cut-off tire of 1/160 and above were found to fall within acceptable ranges for normal healthy individuals. Most patients also had normal leucocytes count values as determined by previous parameters used for healthy persons. The results of this study revealed that the established notion of leucopenia, neutropenia and lymphocytosis common in cases of salmonellosis among people of the Western world and Asians does not hold for Nigerians. It is suffice to infer that peripheral blood leucocytes count as an index of cellular immune response to Salmonella infections is not adequate, as currently used in some Laboratories and clinical centres in the diagnosis of patients with salmonellosis. KEY WORDS: Salmonella typhi, salmonellosis, widal test, leucocyte count, leucopenia, neutropenia, diagnosis. Nigerian Journal of Health and Biomedical Sciences Vol.4(1) 2005: 8-13

Amperometric immunosensor for detection of antibodies of Salmonella typhi in patient serum

An amperometric sensor for detection of antibodies to Salmonella typhi in the serum of patients was developed. This involved usage of screen-printed electrodes and recombinant flagellin fusion protein. An indirect enzyme-linked immunosorbant assay was used for detection of antibodies to S. typhi in the patient serum. The screen-printed electrodes were made using polystyrene and graphite. These electrodes were tested for their ability to detect 1-naphthol, which is the product formed due to the hydrolysis of the substrate 1-naphthyl phosphate by the enzyme alkaline phosphatase. These electrodes were coated with recombinant flagellin fusion protein made by recombinant DNA technology and blocked with bovine serum albumin (BSA). Further they were incubated with patient serum and goat anti-human alkaline phosphatase conjugate. The immunosensing was performed by using amperometric method. Pooled human serum samples from apparently healthy individuals were used as control. Both the pooled healthy human serum samples and patient sera were subjected to Widal agglutination test and amperometric method. A 100% correlation was found between the Widal test and amperometric method. The time taken for the detection by electrochemical method is 1 h and 15 min, while the time taken by Widal test is 18 h.

Open study of short course Fleroxacin for Typhoid and Paratyphoid Fever

The objective of this study was to evaluate clinical and bacteriological effect of short course fleroxacin in uncomplicated typhoid and paratyphoid fever patients. Four hundred mg of fleroxacin was given oraly once daily for a period of 3 to 5 days. The diagnosis of typhoid and paratyphoid fever was established by clinical picture as well as blood culture or Widal serology test. Thirty patients in whom the clinical picture was confirmed as a typhoid or paratyphoid infection were eligible for this investigation. They consisted of 15 males and 15 females ranging in age from 18-38 years average 27.5 years of whom 18 were diagnosed by blood culture consisting of 16 S.typhi positive cases and two S.paratyphi A, while 12 other cases were positively confirmed by serial Widal agglutination serology. These cases suffered from fever between 3-14 days with a minimum recorded body temperature elevation of 38.5 degrees Celsius. Clinical response with defervescence of fever was obtained in the positive blood culture group within 3 days (8 patients) including 2 cases positive for S.paratyphi A and within two additional days (5 days) in the remaining 10 cases. In the twelve cases with a positive serology for typhoid fever a clinical response was obtained for defervescence within 3 days (6 cases) with 4 of these cases were on 3 days of fleroxacin and 2 cases on 5 days of fleroxacin. In the remaining 6 serologic positive cases fever resolved after 4-6 days with an average of 5 days with one on 3 days of fleroxacin and the rest (5 cases) on 5 days of fleroxacin. All positive blood culture cases reverted to negative after the fleroxacin course. No relapse or carrier state was recorded in this serie. It may be concluded that a 3 to 5 days closely monitored course of fleroxacin has excellent clinical as well as bacteriological efficacy in noncomplicated typhoid and paratyphoid fever. (Med J Indones 2002; 11: 41-7) Keywords: fluoroquinolones, enteric infections, short course efficacy, open prospective study

The increase in occurrence of typhoid fever in Cameroon: overdiagnosis due to misuse of the Widal test?

This study investigates the cause of an apparent increase in occurrence of typhoid fever in Cameroon. The reasons explored include an overdiagnosis of the illness related to poor performance of the Widal test in laboratories and interpretation by prescribers. Questionnaires were used in 1996 to evaluate the use and interpretation of the Widal test, and checklists were used to assess its laboratory performance in 2 of the 10 provinces in Cameroon. The majority of prescribers from 20 health facilities (an average of 76% of the doctors and 61% of the nurses) could detect patients who truly had positive Widal tests and needed treatment. However, an average of 48% of the doctors and 84% of the nurses would treat patients who did not require treatment based on the Widal test result. Patients may therefore be treated unnecessarily. Most (88%) of the visited laboratories performed the Widal rapid slide agglutination test as opposed to the conventional tube agglutination test. About 14% of the laboratories that performed the rapid slide agglutination test had a score above average for each criterion evaluated. Misdiagnosis of typhoid fever leads to unnecessary expenditure and exposure of patients to the side-effects of antibiotics. In addition, misdiagnosis may result in delayed diagnosis and treatment of malaria, and other acute febrile illness.

The serodiagnosis of infection with Salmonella typhi

Background/Aims—The serodiagnosis of infection with Salmonella typhi,using the Widal agglutination assay, relies on patients' antibodies to the O=9,12 lipopolysaccharide (LPS) antigens, H=d flagellar antigens, and the Vi capsular antigens. A...