Re-evaluation of the Widal agglutination test in response to the changing pattern of typhoid fever in the highlands of Papua New Guinea

An observational study to compare the diagnostic accuracy of rapid antigen test and rapid antibody tests in various periods of enteric fever

A cross-sectional observational study was done on 180 fever patients to assess the diagnostic accuracy of rapid serological tests in early detection (<5 days of fever) of S. typhi and S. paratyphi in comparison to blood culture and Widal test Blood culture was positive in 58 (32.22%) cases. The diagnostic accuracy (<5 days of fever) of rapid antigen test, rapid antibody test, and Widal test was 45.56%, 42.22%, and 41.11% (p = 0.675) while sensitivity was 68.97%, 48.28%, and 46.55%, respectively. In conclusion, rapid antigen test holds moderately higher sensitivity in the first five days of fever as compared to rapid antibody and Widal tests. It is recommended that the antigen detection tests should be used for screening enteric fever in the first week of presentation.

Enteric Fever Diagnosis: Current Challenges and Future Directions

Enteric fever is a life-threatening systemic febrile disease caused by Salmonella enterica serovars Typhi and Paratyphi (S. Typhi and S. Paratyphi). Unfortunately, the burden of the disease remains high primarily due to the global spread of various drug-resistant Salmonella strains despite continuous advancement in the field. An accurate diagnosis is critical for effective control of the disease. However, enteric fever diagnosis based on clinical presentations is challenging due to overlapping symptoms with other febrile illnesses that are also prevalent in endemic areas. Current laboratory tests display suboptimal sensitivity and specificity, and no diagnostic methods are available for identifying asymptomatic carriers. Several research programs have employed systemic approaches to identify more specific biomarkers for early detection and asymptomatic carrier detection. This review discusses the pros and cons of currently available diagnostic tests for enteric fever, the advancement of research toward improved diagnostic tests, and the challenges of discovering new ideal biomarkers and tests.

Baseline Antibody Titre against Salmonella enterica in Healthy Population of Mumbai, Maharashtra, India

Objective

The aim of this study was to establish a baseline titre for the population of Mumbai, Maharashtra, India.

Method

Four hundred healthy blood donors, attending blood donation camps, were screened using a survey questionnaire. Widal tube agglutination test was performed on the diluted sera (with 0.9% normal saline) of blood donors, with final dilution ranging from 1 : 40 to 1 : 320.

Results

Out of 400 individuals providing samples, 78 (19.5%) individuals showed antibody titres ≥ 1 : 40 for at least one antigen and 322 (80.5%) showed no agglutination. The baseline antibody titres against O antigen and H antigen of Salmonella enterica serotype Typhi were found to be 1 : 40 and 1 : 80, respectively. Similarly, the baseline antibody titres for the H antigen of Salmonella enterica serotypes Paratyphi A and Paratyphi B were found to be 1 : 40 and 1 : 80, respectively.

Conclusion

Thus, it was noted that the diagnostically significant cutoff of antibody titre from acute phase sample was ≥ 1 : 80 for S. Typhi O antigen and titre of ≥ 1 : 160 for both S. Typhi H antigen and S. Paratyphi BH antigen. Antibody titre of ≥ 1 : 80 can be considered significant for S. Paratyphi AH antigen.

A cross-sectional seroepidemiological survey of typhoid fever in Fiji

Fiji, an upper-middle income state in the Pacific Ocean, has experienced an increase in confirmed case notifications of enteric fever caused by Salmonella enterica serovar Typhi (S. Typhi). To characterize the epidemiology of typhoid exposure, we conducted a cross-sectional sero-epidemiological survey measuring IgG against the Vi antigen of S. Typhi to estimate the effect of age, ethnicity, and other variables on seroprevalence. Epidemiologically relevant cut-off titres were established using a mixed model analysis of data from recovering culture-confirmed typhoid cases. We enrolled and assayed plasma of 1787 participants for anti-Vi IgG; 1,531 of these were resident in mainland areas that had not been previously vaccinated against S. Typhi (seropositivity 32.3% (95%CI 28.2 to 36.3%)), 256 were resident on Taveuni island, which had been previously vaccinated (seropositivity 71.5% (95%CI 62.1 to 80.9%)). The seroprevalence on the Fijian mainland is one to two orders of magnitude higher than expected from confirmed case surveillance incidence, suggesting substantial subclinical or otherwise unreported typhoid. We found no significant differences in seropositivity prevalences by ethnicity, which is in contrast to disease surveillance data in which the indigenous iTaukei Fijian population are disproportionately affected. Using multivariable logistic regression, seropositivity was associated with increased age (odds ratio 1.3 (95% CI 1.2 to 1.4) per 10 years), the presence of a pit latrine (OR 1.6, 95%CI 1.1 to 2.3) as opposed to a septic tank or piped sewer, and residence in settlements rather than residential housing or villages (OR 1.6, 95% CI 1.0 to 2.7). Increasing seropositivity with age is suggestive of low-level endemic transmission in Fiji. Improved sanitation where pit latrines are used and addressing potential transmission routes in settlements may reduce exposure to S. Typhi. Widespread unreported infection suggests there may be a role for typhoid vaccination in Fiji, in addition to public health management of cases and outbreaks.

Fiji has experienced a decade-long increase in typhoid fever cases, a potentially life-threatening systemic bacterial disease caused by Salmonella Typhi. We undertook a representative blood-serum community survey to measure antibodies (IgG) against the Vi antigen of Salmonella Typhi using a rigorous survey design. We found one in three residents of mainland, unvaccinated Fiji had detectable antibody against Vi. This was higher than would be expected from confirmed case notifications received by the national surveillance system. Additionally, similar antibody responses were detected in Fijians of all ethnicities, which contrasts to surveillance cases in which indigenous iTaukei Fijians were disproportionately affected. Serology on a Fijian island where a significant proportion of the population has been vaccinated found that three-quarters of residents were seropositive three years after the Vi-polysaccharide typhoid vaccination campaign. Importantly, in mainland participants, seroprevalence increased with age, suggesting long-standing, low-level, endemic transmission. Pit latrines were associated with seropositivity when compared with septic tanks, and settlements compared with residential housing. Very high antibody titres in a small percentage of participants may suggest carriage of Salmonella Typhi. The seroprevalence findings suggest eliminating typhoid from Fiji by focussing on cases and outbreaks alone will be challenging. Our results support typhoid vaccination and further development of water, sanitation and hygiene infrastructure in Fiji.

Study of baseline Widal titres in a healthy adult population of Wayanad district, Kerala, India

The Widal test is still widely used in diagnosing typhoid fever in developing countries. Often, specific chemotherapy is administered based on a single Widal test. Interpretation of a single Widal test, in turn, depends on the baseline agglutinin titres among the local population in that area. Hence, we aimed to find out the baseline titres in our area. A single blood sample was collected from hospital outpatients with non-infectious diseases, the patients being aged above 18 years and residing in Wayanad district continuously for at least 5 years. The test was performed according to the Widal test kit manufacturer's instructions and interpreted using standard guidelines. The baseline titre for Anti TO, TH, AH and BH agglutinins in our area was found to be 1:40, 1:80, 1:40 and 1:40, respectively.

Limitations of typhoid fever diagnostics and the need for prevention

The study under review evaluated serological tests for typhoid fever against PCR as a reference test. While laboratory testing is essential for the confirmation of this severe disease, the low bacterial load and the low level of specific antibodies in the blood of typhoid patients combined with its acute character make interpretation of laboratory testing cumbersome. Validation of an index test requires good understanding of the diagnostic performance and assay characteristics of the reference test, and criteria and principles for study design and reporting outlined by the Quality Assessment of Diagnostic Accuracy Studies and the Standards for Reporting Studies of Diagnostic Accuracy should be followed. Described PCR assays for typhoid fever have not been validated against bone marrow culture, the gold standard, and their diagnostic utility remains to be established.

The baseline widal titre among the healthy individuals of the hilly areas in the garhwal region of uttarakhand, India

INTRODUCTION

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.

MATERIAL AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

Validation of a new serology-based dipstick test for rapid diagnosis of typhoid fever

Currently, no reliable diagnostic test is available for typhoid fever. One serology-based dipstick test, developed indigenously, was validated in this study. Preserved sera from 336 fever patients with known culture results for Salmonella Typhi were blindly tested by the Widal test and the new assay. Analytical sensitivities, specificities, and efficiencies for the new assay versus the Widal test were 68.8% versus 62.5%, 71.1% versus 37.1%, and 70.5% versus 43.2%, respectively (p < 0.001), considering S. Typhi-positive samples as gold standards. Thereafter, fresh sera from 102 hospital-attending children with clinical typhoid fever (including 20 confirmed nontyphoidal cases as control) were tested by both methods and analyzed statistically. The diagnostic sensitivity, specificity, and efficiency were 51.2%, 85%, and 57.8% for the new assay, and 43.9%, 65%, and 48% for the Widal test, respectively. Overall performance ability of the new assay was not better than the Widal test (p > 0.5). Further improvement of the new point-of-care typhoid assay is recommended before implementation in the field setup.

The dilemma of widal test - which brand to use? a study of four different widal brands: a cross sectional comparative study

BACKGROUND

Serodiagnosis of typhoid fever by Widal test based on demonstrating the presence of agglutinins (antibodies) in the serum of an infected patient, against the H (flagellar) and O (somatic) antigens of Salmonella enterica serotype Typhi has been associated with many debates. This is why the aim of this study was to: (i) Compare the diagnostic accuracy of four different commercial kits used to perform Widal test (Remel, BioSystems, Dialab and Biotec). (ii) Compare the sensitivity and specificity of both anti-O and anti-H antibodies. (iii) Compare the validity of single versus paired serum samples with a rising titer for the diagnosis of typhoid fever.

METHODS

Duplicate serum samples were obtained from 150 patients clinically diagnosed as typhoid fever patients. Moreover, single serum samples were obtained from 25 patients with febrile diseases other than typhoid fever. All samples were tested using the four different Widal brands and Salmonella Typhi IgM anti-LPS ELISA.

RESULTS

-The results of Widal tests differed markedly using the four Widal brands in terms of sensitivity and specificity at three cut-off values of 1/80, 1/160 and 1/320. Remel brand gave the highest sensitivities and the lowest specificities and Dialab brand gave the highest specificities and the lowest sensitivities for both anti-O and anti-H antibodies at the three cut-off values.-Four fold rise in the antibodies titer was not demonstrable among clinically diagnosed typhoid fever patients-H agglutinins were less sensitive and less specific than O agglutinins

CONCLUSIONS

-Widal test results showed marked discrepancies using different Widal brands. None of the serum samples of the typhoid fever patients showed four fold rise in the antibody titers. Raised O agglutinins were of slightly greater diagnostic value than raised H agglutinins.

SIGNIFICANCE AND IMPACT OF STUDY

Widal test done sequentially using two brands could be of value in typhoid fever diagnosis. Single serum sample could be used for typhoid fever diagnosis relying on anti O titer.

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

Background

Enteric 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.

Methods

We 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.

Results

Among 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.

Conclusion

When 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.

Optimizing typhoid fever case definitions by combining serological tests in a large population study in Hechi City, China

Blood culture-based diagnosis can only detect a fraction of the total burden of Salmonella enterica subsp. enterica serovar Typhi. The objective of the study was to detect additional typhoid fever cases through serological tests. A total of 1732 prolonged fever episodes were evaluated using three serological tests, Widal, Tubex and Typhidot-M in a typhoid fever endemic area of southern China. A case definition which included a positive Widal test (TO>or=80 & TH>A), a positive Tubex test (>or=4) and a positive Typhidot-M test, increased the detection of cases by more than twofold from 13 to 28 cases. The case definition has a specificity of 100% and a sensitivity of 39%. Case definitions based on combinations of serological tests can detect additional typhoid fever cases with higher specificity than a single serological test. Improved case detection is essential to understand the true disease burden and can help to boost the power of intervention trials.

The distribution of anti-Salmonella antibodies in the sera of blood donors in Yaoundé, Cameroon

This cross-sectional study in late 1996 on a group of 230 consecutive blood donors in Yaoundé, Cameroon, found a baseline titre of 1:100 for antisalmonella O antibodies. The seroprevalence and baseline titre for antisalmonella H antibodies was much higher (1:400), suggesting that the H antibody is of limited diagnostic value in Cameroon.

Value of a single-tube widal test in diagnosis of typhoid fever in Vietnam

The diagnostic value of an acute-phase single-tube Widal test for suspected typhoid fever was evaluated with 2,000 Vietnamese patients admitted to an infectious disease referral hospital between 1993 and 1998. Test patients had suspected typhoid fever and a blood culture positive for Salmonella typhi (n= 1,400) or Salmonella paratyphi A (n = 45). Control patients had a febrile illness for which another cause was confirmed (malaria [n = 103], dengue [n = 76], or bacteremia due to another microorganism [n = 156] or tetanus (n = 265). An O-agglutinin titer of >/=100 was found in 18% of the febrile controls and 7% of the tetanus patients. Corresponding values for H agglutinins were 8 and 1%, respectively. The O-agglutinin titer was >/=100 in 83% of the blood culture-positive typhoid fever cases, and the H-agglutinin titer was >/=100 in 67%. The disease prevalence in investigated patients in this hospital was 30.8% (95% confidence interval, 26.8 to 35.1%); at this prevalence, an elevated level of H agglutinins gave better positive predictive values for typhoid fever than did O agglutinins. With a cutoff titer of >/=200 for O agglutinin or >/=100 for H agglutinin, the Widal test would diagnose correctly 74% of the blood culture-positive cases of typhoid fever. However, 14% of the positive results would be false-positive, and 10% of the negative results would be false-negative. The Widal test can be helpful in the laboratory diagnosis of typhoid fever in Vietnam if interpreted with care.

Monoclonal antibodies directed against unique and common determinants on the lipopolysaccharide molecule of Salmonella serogroups A, B, and D

A panel of monoclonal antibodies (MAbs) directed against lipopolysaccharide (LPS) of Salmonella serogroups A, B, and D was generated. Nine most productive hybrid clones were selected from several fusions of mouse myeloma cells with splenocytes from BALB/c mice, immunized with the corresponding heat-killed bacteria. The MAbs were characterized by enzyme immunoassay, Western blot analysis, and dot-immunoblotting with LPS and whole bacteria of Salmonella serogroups A-E and some other representatives of the Enterobacteriaceae family. Seven MAbs were reactive with the sole Salmonella strain used as an immunogen; one MAb, SD:10D9H, reacted with the five major serogroups of Salmonella species (A, B, D, E1, and E2); and one MAb, SA:5D12A, reacted with Salmonella serogroups A-E and a rough strain of S. cholerae-suis. None of the MAbs reacted with LPS of E. coli 055:B5 or whole bacteria of E. coli K12, Klebsiella pneumoniae, or Proteus vulgaris. The typical ladder-like patterns of bands were observed after immunoblotting of MAbs against electrophoretically resolved LPS from Salmonella serogroups A-E, which thus confirmed their LPS-directed specificity. MAbs affinity constants were determined by noncompetitive enzyme immunoassay using serial dilutions of both LPS as antigen (coating the plate) and antibodies. On the base of the results obtained, the presumed epitopes for each of the MAbs were discussed. The usefulness of MAbs generated for diagnostic and protective purposes was declared.