The TUBEX test detects not only typhoid-specific antibodies but also soluble antigens and whole bacteria

A large and persistent outbreak of typhoid fever caused by consuming contaminated water and street-vended beverages: Kampala, Uganda, January - June 2015

Background

On 6 February 2015, Kampala city authorities alerted the Ugandan Ministry of Health of a “strange disease” that killed one person and sickened dozens. We conducted an epidemiologic investigation to identify the nature of the disease, mode of transmission, and risk factors to inform timely and effective control measures.

Methods

We defined a suspected case as onset of fever (≥37.5 °C) for more than 3 days with abdominal pain, headache, negative malaria test or failed anti-malaria treatment, and at least 2 of the following: diarrhea, nausea or vomiting, constipation, fatigue. A probable case was defined as a suspected case with a positive TUBEX® TF test. A confirmed case had blood culture yielding Salmonella Typhi. We conducted a case-control study to compare exposures of 33 suspected case-patients and 78 controls, and tested water and juice samples.

Results

From 17 February–12 June, we identified 10,230 suspected, 1038 probable, and 51 confirmed cases. Approximately 22.58% (7/31) of case-patients and 2.56% (2/78) of controls drank water sold in small plastic bags (OR_M-H = 8.90; 95%CI = 1.60–49.00); 54.54% (18/33) of case-patients and 19.23% (15/78) of controls consumed locally-made drinks (OR_M-H = 4.60; 95%CI: 1.90–11.00). All isolates were susceptible to ciprofloxacin and ceftriaxone. Water and juice samples exhibited evidence of fecal contamination.

Conclusion

Contaminated water and street-vended beverages were likely vehicles of this outbreak. At our recommendation authorities closed unsafe water sources and supplied safe water to affected areas.

Electronic supplementary material

The online version of this article (doi:10.1186/s12889-016-4002-0) contains supplementary material, which is available to authorized users.

Identification of B-cell Epitope of Leishmania donovani and its application in diagnosis of visceral leishmaniasis

Diagnosis of visceral leishmaniasis (VL) is often hindered by cross-reactions with antigens from other related parasite infections. This study aimed to develop an immunochromatographic test (ICT) which can detect the antigen present in circulating immune complexes (CICs) of VL patients using B-cell epitope-specific antibodies. MS analysis of six immunoreactive 2DE spots revealed two epitopes i.e. RFFVQGDGIGQHSLQEALERR (P₁) and RRVAVLVLLDRL (P₂) (From a hypothetical protein [Acc No: XP_003861458.1]). The epitope conservancy analysis suggested that the linear epitope (P₁P₂) is 97-100% conserved among Leishmania species and diverged from Homo sapiens (61% query coverage and 80% identity). Further, immunoinformatics analysis of hydrophilicity and flexibility confirmed the antigenicity of the peptide fragment. The linear epitope (P₁P₂) was synthesized (98% purity) and the purity was confirmed by high-performance liquid chromatography and MS. The indirect Enzyme linked immunosorbent assay results confirmed the presence of the corresponding antibody in VL patient's sera but not in those of healthy and other diseases. The result demonstrated a sensitivity 90%; Se Cl95% (82.16-96.27)% and specificity 100%; Sp Cl95% (84.56-100)% which indicated the possibility to be used as a diagnostic tool. Sensitivity, specificity, and diagnostic efficiency of colloidal gold conjugated anti-P₁P₂ antibody ICT strip was 100, 95.2, and 96.7%, respectively, which is slightly better as compared to other ICT for VL. Though, our result indicated the utility of anti-P₁P₂ antibody to detect CICs epitopes, a large-scale inspection in endemic and non-endemic area and in different ethnic population is needed for its validation and authentication.

Typhidot - A blessing or a menace

Objectives:

Typhoid remain an increasing problem in Third world countries like Pakistan. A reliable, easy and affordable rapid diagnostic test is a need for our clinicians, many of whom consider Typhidot to be promising. Typhidot has been used as the only tool to diagnose typhoid fever by general practitioners and consultants despite its low sensitivity and specificity causing misdiagnosis and treatment. We therefore conducted this study to evaluate the sensitivity and specificity of Typhidot in patients with fever.

Methods:

A retrospective analysis of a total of 145 febrile patients was done. Blood culture and Typhidot along with other relevant investigations had been performed in each case. Sensitivity, specificity and the association of Typhidot to the diagnosis was found using SPSS v16.0.

Results:

Out of 145 patients, 15(10.3%) had positive blood culture for Salmonella typhi, 7 (4.8%) had positive culture for salmonella paratyphi and 94(64.8%) had positive culture for other organisms. Twenty nine (20%) patients had negative culture results. Forty seven (32.4%) patients had only IgM positive on Typhidot, 7(4.8%) had both IgM and IgG positive and 91(62.8%) had both IgM and IgG negative. Amongst the 130 patients with diseases other than typhoid, 50(38.5%) showed a positive Typhidot result. Amongst the 15 patients with typhoid, 11(73.3%) showed a negative Typhidot result. The sensitivity of Typhidot was found to be 26.7% and the specificity was 61.5%. The Positive Predictive Value (PPV) was 7.4% and the Negative Predictive Value (NPV) was 87.9%.

Conclusion:

Even though Typhidot is rapid, easy and affordable, its use should be discouraged due to low sensitivity and specificity and insignificant (p=0.067) association to the disease.

Modification of clearview tuberculosis (TB) enzyme-linked immunosorbent assay for TB patients not infected with HIV

Diagnosis of active tuberculosis by detection of urinary lipoarabinomannan (uLAM) from Mycobacterium tuberculosis is an attractive approach. Concentrating urine 100-fold allowed quantitation of uLAM at levels equal to picograms/ml of nonconcentrated urine. The approach of concentrating urine 100-fold improved the clinical sensitivity of the Clearview TB enzyme-linked immunosorbent assay (ELISA) from 7% to 57% yet impaired its specificity from 97% to 89%. (This study has been registered at University Hospital of Turku under registration no. 47/180/2009, Helsinki University Central Hospital under 149/2010, University Hospital of Kuopio under 105/2010, and China Medical University Hospital, Taichung, under DMR-99-IRB-075-2.).

Microbiological culture simplified using anti-O12 monoclonal antibody in TUBEX test to detect Salmonella bacteria from blood culture broths of enteric fever patients

Definitive diagnosis of infectious diseases, including food poisoning, requires culture and identification of the infectious agent. We described how antibodies could be used to shorten this cumbersome process. Specifically, we employed an anti-Salmonella lipopolysaccharide O12 monoclonal antibody in an epitope-inhibition 10-min test (TUBEX TP) to detect O12⁺Salmonella organisms directly from routine blood culture broths. The aim is to obviate the need to subculture the broth and subsequently identify the colonies. Thus, blood from 78 young outpatients suspected of having enteric fever was incubated in an enrichment broth, and after 2 or 4 days, broth samplings were examined by TUBEX TP as well as by conventional agar culture and identification. TUBEX TP was performed before the culture results. Eighteen isolates of S. Typhi (15 after 2 days) and 10 isolates of S. Paratyphi A (4 after 2 days) were obtained by conventional culture. Both these Salmonella serotypes, the main causes of enteric fever, share the O12 antigen. In all instances where either of these organisms was present (cultured), TUBEX TP was positive (score 4 [light blue] – to – score 10 [dark blue]; negative is 0 [pink-colored]) i.e. 100% sensitive. Identification of the specific Salmonella serotype in TUBEX-positive cases was achieved subsequently by conventional slide agglutination using appropriate polyclonal antisera against the various serotypes. Twelve Escherichia coli, 1 Alcaligenes spp. and 1 Enterobacter spp. were isolated. All of these cases, including all the 36 culture-negative broths, were TUBEX-negative i.e. TUBEX TP was 100% specific. In a separate study using known laboratory strains, TUBEX TF, which detects S. Typhi but not S. Paratyphi A via the O9 antigen, was found to efficiently complement TUBEX TP as a differential test. Thus, TUBEX TP and TUBEX TF are useful adjuncts to conventional culture because they can save considerable time (>2 days), costs and manpower.

Evaluation of a simple blood culture amplification and antigen detection method for diagnosis of Salmonella enterica serovar typhi bacteremia

In most areas where typhoid is endemic, laboratory diagnosis is not possible due to the lack of appropriate facilities. We investigated whether the combination of blood culture amplification of Salmonella enterica serovar Typhi with an S. Typhi antigen rapid diagnostic test (RDT) could be an accurate and inexpensive tool for the accelerated diagnosis of patients with acute typhoid in Laos. For a panel of 23 Gram-negative reference pathogens, the Standard Diagnostics (catalog no. 15FK20; Kyonggi-do, South Korea) RDT gave positive results for S. Typhi NCTC 8385, S. Typhi NCTC 786 (Vi negative), Salmonella enterica serovar Enteritidis (ATCC 13076), and Salmonella enterica serovar Ndolo NCTC 8700 (all group D). In a prospective study of 6,456 blood culture bottles from 3,028 patients over 15 months, 392 blood culture bottles (6.1%) from 221 (7.3%) patients had Gram-negative rods (GNRs) seen in the blood culture fluid. The sensitivity, negative predictive value, specificity, and positive predictive value were 96.7%, 99.5%, 97.9%, and 87.9%, respectively, for patients with proven S. Typhi bacteremia and 91.2%, 98.4%, 98.9%, and 93.9% for patients with group D Salmonella. The median (range) number of days between diagnosis by RDT and reference assays was 1 (-1 to +2) day for those with confirmed S. Typhi. The use of antigen-based pathogen detection in blood culture fluid may be a useful, relatively rapid, inexpensive, and accurate technique for the identification of important causes of bacteremia in the tropics.

Sensitivity and specificity of typhoid fever rapid antibody tests for laboratory diagnosis at two sub-Saharan African sites

OBJECTIVE

To evaluate three commercial typhoid rapid antibody tests for Salmonella Typhi antibodies in patients suspected of having typhoid fever in Mpumalanga, South Africa, and Moshi, United Republic of Tanzania.

METHODS

The diagnostic accuracy of Cromotest(®) (semiquantitative slide agglutination and single tube Widal test), TUBEX(®) and Typhidot(®) was assessed against that of blood culture. Performance was modelled for scenarios with pretest probabilities of 5% and 50%.

FINDINGS

In total 92 patients enrolled: 53 (57.6%) from South Africa and 39 (42.4%) from the United Republic of Tanzania. Salmonella Typhi was isolated from the blood of 28 (30.4%) patients. The semiquantitative slide agglutination and single-tube Widal tests had positive predictive values (PPVs) of 25.0% (95% confidence interval, CI: 0.6-80.6) and 20.0% (95% CI: 2.5-55.6), respectively. The newer typhoid rapid antibody tests had comparable PPVs: TUBEX(®), 54.1% (95% CI: 36.9-70.5); Typhidot(®) IgM, 56.7% (95% CI: 37.4-74.5); and Typhidot(®) IgG, 54.3% (95% CI: 36.6-71.2). For a pretest probability of 5%, PPVs were: TUBEX(®), 11.0% (95% CI: 6.6-17.9); Typhidot(®) IgM, 9.1% (95% CI: 5.8-14.0); and Typhidot(®) IgG, 11.0% (6.3-18.4). For a pretest probability of 50%, PPVs were: TUBEX(®), 70.2% (95% CI: 57.3-80.5); Typhidot(®) IgM, 65.6% (95% CI: 54.0-75.6); and Typhidot(®) IgG, 70.0% (95% CI: 56.0-81.1).

CONCLUSION

Semiquantitative slide agglutination and single-tube Widal tests performed poorly. TUBEX(®) and Typhidot(®) may be suitable when pretest probability is high and blood cultures are unavailable, but their performance does not justify deployment in routine care settings in sub-Saharan Africa.

Assessment and comparative analysis of a rapid diagnostic test (Tubex®) for the diagnosis of typhoid fever among hospitalized children in rural Tanzania

Background

Typhoid fever remains a significant health problem in many developing countries. A rapid test with a performance comparable to that of blood culture would be highly useful. A rapid diagnostic test for typhoid fever, Tubex^®, is commercially available that uses particle separation to detect immunoglobulin M directed towards Salmonella Typhi O9 lipopolysaccharide in sera.

Methods

We assessed the sensitivity and specificity of the Tubex test among Tanzanian children hospitalized with febrile illness using blood culture as gold standard. Evaluation was done considering blood culture confirmed S. Typhi with non-typhi salmonella (NTS) and non - salmonella isolates as controls as well as with non-salmonella isolates only.

Results

Of 139 samples tested with Tubex, 33 were positive for S. Typhi in blood culture, 49 were culture-confirmed NTS infections, and 57 were other non-salmonella infections. Thirteen hemolyzed samples were excluded. Using all non - S. Typhi isolates as controls, we showed a sensitivity of 79% and a specificity of 89%. When the analysis was repeated excluding NTS from the pool of controls we showed a sensitivity of 79% and a specificity of 97%. There was no significant difference in the test performance using the two different control groups (p > 0.05).

Conclusion

This first evaluation of the Tubex test in an African setting showed a similar performance to those seen in some Asian settings. Comparison with the earlier results of a Widal test using the same samples showed no significant difference (p > 0.05) for any of the performance indicators, irrespective of the applied control group.

Modification of the TUBEX typhoid test to detect antibodies directly from haemolytic serum and whole blood

The TUBEX test for typhoid fever detects serum antibodies in a simple and rapid assay system based on the inhibition of binding between two types of reagent particles - magnetic particles coated with an antigen (Salmonella O9 LPS) and coloured indicator particles coated with an anti-O9 mAb. A magnet is used to separate the colour indicator particles bound to the magnetic particles from the unbound indicator particles. Specific colour changes following magnetic separation are indicative of antibodies in the patient's serum; however, because results are interpreted based on changes in the colour red, haemolytic or icteric specimens cannot be used. This study describes a simple modification of the protocol to accommodate such specimens, including whole blood. This involves the addition of a quick and simple washing step after mixing the specimen with the antigen-bound magnetic particles. This modification has the advantage of allowing larger sample volumes to be used, thus enhancing the assay sensitivity, and also enables cases considered to be borderline positive by the original method to be re-assessed.