Stool Antigen Testing, a Reliable Noninvasive Method of Assessment of Helicobacter pylori Infection Among Patients with Gastro-duodenal Disorders in Cameroon.

BACKGROUND: Several techniques such as invasive and noninvasive are used for the diagnosis of H. pylori infection. AIM: The aim of this study was to compare the results of rapid urease test, stool antigen test and serology in diagnosing H. pylori infection in Cameroon. METHODS: Hundred patients (66 women and 34 men) were enrolled. Each patient gave a written consent. The study was approved by the local Ethical Committee of Medical Sciences and the institutional review board. From each patient, blood, stool and gastric biopsies samples were collected for H. pylori detection using three methods: stool antigen test, serology and rapid urease test (RUT), taken as gold standard. Statistical analysis was performed using Graph pad Prism 7. RESULTS: Helicobacter pylori infection was detected in 43%, 45% and 73% of patients based on the RUT, stool antigen test and serology, respectively. The difference was statistically significant between serology and RUT (P = 0.0026), but not between stool antigens test and RUT (P = 0.288). Taken RUT as gold standard, the sensitivity, specificity, positive and negative predictive values of stool antigens test and serology were 65.11, 70.17, 62.22 and 72.72%; 88.37, 40.35, 55.77 and 82.14%, respectively. The accuracy of stool antigen test and serology was 68 and 61%, respectively. CONCLUSIONS: Our finding showed that stool antigen test can be used as a noninvasive method of assessment of H. pylori infection in our setting. Serological test can be used in screening; however, further diagnostic tests need to be carried out to confirm seropositive cases.

The Diagnostic Tests for Detection of Helicobacter pylori Infection.

Helicobacter pylori causes one of the most common infections in human populations. The role of this bacterium in chronic gastritis, gastric ulcer, gastric cancer, as well as extra-digestive diseases such as ischemic heart disease and chronic obstructive pulmonary diseases, is well known. Prevention and control of these diseases can occur by early diagnosis and eradication of H. pylori infection. At present, different methods have been established to detect H. pylori infection. The biopsy-based tests, which are known as invasive methods, such as rapid urease test and histology, have the highest specificity among the others. Similarly, culture of biopsy samples is used for diagnosis of H. pylori infection. It has a high specificity value, and also allows us to perform antibiotic sensitivity testing. On the contrary, polymerase chain reaction and other molecular methods have good sensitivity and specificity, and can be used for detection of H. pylori infection, its virulence factors, and eradication success after treatment. While serological tests are more appropriate for epidemiological studies, their main weakness for clinical use is low specificity. Overall, specificity and sensitivity, cost, usefulness, and limitation of tests should be considered for selection of detection methods of H. pylori in each country.

Multiplex serology of Helicobacter pylori antigens in detection of current infection and atrophic gastritis - A simple and cost-efficient method.

INTRODUCTION: Helicobacter pylori express a large array of antigens, each of which is duly responsible for successful colonization and pathogenesis. Here, we have studied host serum antibody responses to four of its immunodominant antigens in association with the infection status and the resulting clinical outcomes. METHODS: For this purpose, four individual H. pylori proteins (UreB, CagA, Tip-α and HP0175) were produced in recombinant forms. Serum antibody responses of 246 (75 GC and 171 NUD) patients, against the above antigens, were evaluated by multiplex immunoblotting. The associations between the resulting data and the infection status, as well as clinical outcomes were evaluated using logistic regression models. RESULTS: Serum antibodies to all four recombinant antigens increased the chances of detecting screening ELISA-positive subjects, in an escalating dose-dependent manner, ranging from 2.6 (1.5-4.7) for HP0175 to 14.3 for UreB (4.3-50.7), exhibiting the lowest and highest odds ratios, respectively (PAdj ≤ 0.001), such that 98.2% of the subjects with antibodies to all four antigens, were also positive by the screening ELISA (P < 0.0001). Among the screening ELISA-positive subjects, the three antigens of CagA, Tip-α, and HP0175 were able to segregate current from past H. pylori infection (P < 0.05). Accordingly, subjects with antibodies to one or more antigen(s) were at 5.4 (95% CI: 1.8-16.4) folds increased chances of having current infection, as compared to triple negatives (PAdj = 0.003). In reference to the clinical outcomes, those with serum antibodies to CagA were more prevalent among gastric cancer, as compared to NUD patients (ORAdj: 5.4, 95% CI: 2.4-12.2, PAdj < 0.0001). When NUD patients were categorized according to their histopathologic status, multiple antigen analysis revealed that subjects with serum antibodies to one or more of the 3 current infection-positive antigens (CagA, Tip-α, and HP0175) were at 9.7 (95% CI: 2.1-44.9, P = 0.004) folds increased risk of atrophic gastritis, in reference to triple negatives. CONCLUSION: The non-invasive multiplex serology assay, presented here, was able to not only detect subjects with current H. pylori infection, it could also screen dyspeptic patients for the presence of gastric atrophy. This simple and cost-efficient method can supplement routine screening ELISAs, to increase the chances of detecting current infections as well as atrophic gastritis.

Assessment of a protein cocktail-based skin test for bovine tuberculosis in a double-blind field test in cattle.

Bovine tuberculosis (bTB) is a worldwide zoonosis caused mainly by Mycobacterium bovis. The traditional diagnostic method used often is the tuberculin skin test, which uses bovine purified protein derivatives (PPD-B). However, it is difficult to maintain uniformity of PPD-B from batch to batch, and it shares common antigens with nonpathogenic environmental mycobacteria. To overcome these problems, M. bovis-specific antigens that showed good T cell stimulation, such as CFP-10, ESAT-6, Rv3615c, etc., have been used in the skin test, but there have been no large-scale clinical studies on these antigens. In this study, two combinations (CFP-10/ESAT-6/TB10.4 protein cocktail and CFP-10/ESAT-6/Rv3872/MPT63 protein cocktail) were developed and used as stimuli in the skin test. Cattle were double-blind tested to assess the efficiency of the protein cocktail-based skin tests. The results showed that the CFP-10/ESAT-6/TB10.4 protein cocktail-based skin test can differentiate TB-infected cattle from Mycobacterium avium-infected ones and that it shows a high degree of agreement with the traditional tuberculin skin test (κ = 0.8536) and gamma interferon (IFN-γ) release assay (κ = 0.8154). Compared to the tuberculin skin test, the relative sensitivity and relative specificity of the CFP-10/ESAT-6/TB10.4-based skin test were 87% and 97%, respectively., The relative sensitivity and relative specificity of the CFP-10/ESAT-6/TB10.4-based skin test were 93% and 92%, respectively, on comparison with the IFN-γ release assay. The correlation between the increases in skin thickness observed after the inoculation of stimuli was high (PPD-B versus CFP-10/ESAT-6/TB10.4, Spearman r of 0.8435). The correlation between the optical density at 450 nm (OD450) obtained after blood stimulation with PPD-B and the increase in skin thickness observed after inoculation of the CFP-10/ESAT-6/TB10.4 protein cocktail was high (Spearman r = 0.7335). Therefore, the CFP-10/ESAT-6/TB10.4-based skin test responses correlate to traditional measures of bovine TB evaluation, including skin test and gamma interferon release assay.

There is need for antigen-based rapid diagnostic tests to identify common acute tropical illnesses.

Enteric fever, typhus, leptospirosis, dengue, melioidosis, and tuberculous meningitis present urgent diagnostic problems that require experience and clinical judgment to make early evidence-based management decisions. Basic and applied research dealing with reliable antigen-based diagnostics has been published and confirmed for several of these infections. This should have initiated commercial production but has not. Established international firms see little profit in such diagnostic kits since they would be used in poor countries with little prospects for return of investment capital. We attempt to illustrate this issue, using common causes of acute febrile illnesses in the Southeast Asian region. We believe that rapid diagnostic technology could prevent significant delay in starting appropriate therapy, reduce hospital expenses, and even save lives.

Which test is best for Helicobacter pylori? A cost-effectiveness model using decision analysis.

GPs face a potential dilemma in deciding which test to use for detection of Helicobacter pylori. For patients with dyspepsia, the National Institute for Health and Clinical Excellence (NICE) advises primary care practitioners to adopt a 'test and treat' policy before considering a referral for gastroscopy. There are many ways of testing: serology, urea breath test, and faecal antigen test. NICE does not advocate any preferred single test for detecting H. pylori. In the current study a multi-stakeholder 2-day workshop was established to agree and populate a cost-effectiveness decision analysis model. The aim was to analyse the three types of tests available for H. pylori and to determine which is the most practical and cost effective. Agreement on the costs and diagnostic values to be entered into the decision-analytic model was achieved. Results indicate that the faecal antigen test was the most effective in terms of true outcomes and cost. One thousand virtual patients were allocated to each of the three tests. Serology had 903, urea breath test had 961, and the faecal antigen test had 968 true positive outcomes. Data indicate that the faecal antigen test is the preferable strategy for diagnosis of H. pylori in primary care. This has implications for implementing new testing processes and for commissioning new diagnostic pathways for use in primary care.

An indirect enzyme-linked immunosorbent assay for rapid and quantitative assessment of Type III virulence phenotypes of Pseudomonas aeruginosa isolates.

BACKGROUND: The presence of a Type III secretion system in clinical isolates of Pseudomonas aeruginosa is associated with severe disease and poor outcomes in infections caused by this pathogen. We describe an indirect enzyme-linked immunosorbent assay that rapidly and quantitatively detects two exotoxins, ExoU and ExoT, and two structural components, PopD and PcrV, of the P. aeruginosa Type III secretion system after in-vitro growth in a calcium-free minimal medium. METHODS: We used this assay to characterize the Type III secretion phenotype of 74 clinical isolates of P. aeruginosa. Findings were compared with results of standard immunoblotting and correlated with Type III secretion-dependent virulence of isolates toward cultured epithelial cells. RESULTS: Results of the ELISA assay were concordant with immunoblot detection of the secreted antigens for 73 of 74 isolates. The Type III secretion phenotype assessed by this immunoassay predicted bacterial virulence toward epithelial cells in vitro for all but five of the clinical isolates. CONCLUSION: The availability of an ELISA assay for rapid detection of Type III secreted virulence factors will facilitate large clinical studies to examine whether the Type III secretion phenotype of a P. aeruginosa isolate predicts the course of clinical disease in a patient and should be taken into account in determining optimal treatment strategies for infected patients.

Evaluation of a near-patient fecal antigen test for the assessment of Helicobacter pylori status.

The assessment of Helicobacter pylori antigen in stool specimens is widely accepted. Recently a immunochromatographic near-patient test assay has been developed. In this first evaluation in 100 patients before and after H. pylori eradication therapy we observed a sensitivity (76%) and specificity (98%) of this near-patient test.

Prevalence of Helicobacter pylori infection among low socio-economic workers.

Epidemiological studies have shown that the prevalence of Helicobacter pylori infection in a community and occupational health are closely related to lifestyle and socio-economic status. There is little information on H. pylori profile in industrial workers in the literature. The aim of this study was to investigate the prevalence rate of H. pylori profiles among low socio-economic workers in the United Arab Emirates (UAE). This study was undertaken by determining IgG H. pylori antibody profiles among industrial exposed and referent workers, sera. Presence of anti-H. pylori antibodies in the frozen stored sera was determined by ELISA. Also, data on dietary and lifestyle were obtained. The result was considered positive if IgG anti-H. pylori antibody titers was > 300. People with seropositive levels of IgG antibodies to H. pylori were assumed to be infected with H. pylori. Most of the industrial workers lived in less modern accommodation, were less educated, ate their vegetable products unwashed and did not have drinking water facilities, when compared to referents. H. pylori serology by IgG was positive in 167 industrial workers (78.4%) and 137 in referent workers (64.3%) respectively, (p < 0.002). The sensitivity and specificity of the IgG serology assay were 94.5%, and 97.2% respectively. There was statistically significant difference between the exposed industrial and non-exposed control groups in respect of their H. pylori profiles.

Are follow-up throat cultures necessary when rapid antigen detection tests are negative for group A streptococci?

The frequency of obtaining false-negative Group A Streptococcal (GAS) rapid antigen detection (RAD) tests utilizing currently available kits in a private practice setting and the cost effectiveness of requiring follow-up throat cultures were studied. Laboratory records of the Elmwood Pediatric Group (EPG), Rochester, NY, were retrospectively reviewed to identify all patients with pharyngeal RAD tests for GAS performed from January 1996 through May 1999. From January 1996 through October 1997 (study period 1), EPG physicians used either a RAD test or a throat culture to identify GAS; from November 1997 through May 1999 (study period 2), RAD tests were used as the primary test on all patients. Rapid antigen detection test negative results were confirmed with culture. During the 3-year study 11,427 RAD tests were performed. 8,385 (73.4%) were negative and 3,042 (26.6%) were positive. In study period 1, 3,547 (73.2%) were negative and 1,299 (26.8%) were positive; in study period 2 4,837 (73.5%) were negative and 1,743 (26.5%) were positive. Of the 8,385 negative tests, 8,234 (98.2%) were followed up with throat cultures. Of these, 200 (2.4%) were identified to have been negative RAD tests that were throat culture positive (132 [3.8%] of 3,474 in study period 1 and 68 [1.4%] of 4,764 in study period 2). A cost analysis was performed for study period 2, which showed that abandoning throat culture confirmation would generate a cost saving of $13,521 per year to the practice. Throat culture confirmation of RAD test negative results in pharyngitis patients may not be medically necessary for most patients with currently available RAD tests and is costly.

Accurate diagnosis of Helicobacter pylori. Stool tests.

From the limited data available, it seems that the H. pylori stool assay represents a highly accurate diagnostic tool to detect H. pylori infection before and shortly after therapy. As a test that is noninvasive, accurate, simple, and cost-effective, the H. pylori stool assay has the potential to become the preferred diagnostic tool in many different clinical settings from epidemiologic studies to pediatric investigations, from pre-endoscopic screening policies to posttherapy monitoring.

Management of sore throats in children: a cost-effectiveness analysis.

OBJECTIVE: To perform a cost-effectiveness analysis of treatment management strategies for children older than 3 years who present with signs or symptoms of pharyngitis. DESIGN: Decision model with 7 strategies, including neither testing for streptococcus nor treating with antibiotics; treating empirically with penicillin V; basing treatment on results of a throat culture (Culture); and basing treatment on results of enzyme immunoassay or optical immunoassay rapid tests, performed alone or in combination with throat cultures. In these 7 strategies, all tests are performed in a local reference laboratory. In a sensitivity analysis, we examined the cost-effectiveness of 4 strategies involving office-based testing. We obtained data on event probabilities and test characteristics from our hospital's clinical laboratory and the literature; costs for the analysis were based on resource use. RESULTS: At a baseline prevalence of 20.8% for streptococcal pharyngitis, the Culture strategy was the least expensive and most effective, with an average cost of $6.85 per patient. The outcome was sensitive to the prevalence of streptococcal pharyngitis, the rheumatic fever attack rate, the cost of the enzyme immunoassay test, and the cost of culturing and reporting culture results. The Culture strategy was also preferred if amoxicillin was substituted for oral penicillin. For office-based testing, Culture was the least costly strategy, but treatment based on results of the optical immunoassay test alone had an incremental cost-effectiveness ratio of $1.6 million per additional life saved. CONCLUSION: In a setting with adherent patients, children with sore throats should generally get throat cultures in lieu of rapid streptococcus antigen tests.

Helicobacter pylori and gastric cancer: what are the benefits of screening only for the CagA phenotype of H. pylori?

BACKGROUND: Strains of Helicobacter pylori that express the CagA protein are associated with a threefold increased gastric cancer risk as compared to H. pylori strains that do not express CagA. Screening and treatment only for CagA antibodies should target those individuals at highest gastric cancer risk while reducing the number of patients requiring antibiotics. We compared the costs and benefits of screening asymptomatic 50-year-old individuals for CagA, screening for all H. pylori strains, and no screening, both in the United States and abroad. MATERIALS AND METHODS: We employed Markov cost-effectiveness analysis using data from randomized, case-control, and cohort studies. RESULTS: In the United States, CagA screening would result in 1.5 million fewer antibiotic treatments but would prevent 1,400 fewer gastric cancers than would screening for all H. pylori. The incremental cost-effectiveness of CagA screening is $23,900 per life-year gained; for H. pylori screening, it is $25,100. Screening in countries with epidemiological characteristics similar to those of Colombia, Finland, and Japan costs less than $5,000 per life-year gained, and the difference between CagA and H. pylori screening is smaller than that in the United States. CONCLUSIONS: Screening only for CagA-positive H. pylori is not substantially better than is screening for all H. pylori, either in the United States nor abroad. Screening is substantially more cost-effective outside the United States. Whether population screening is justified, however, is uncertain pending conclusive data regarding the reduction in gastric cancer risk from antibiotics.

Office diagnosis and management of group A streptococcal pharyngitis employing the rapid antigen detecting test. A 1-year prospective study of reliability and cost in primary care centres.

The impact of introducing the rapid antigen detecting test for the diagnosis of group A streptococcal pharyngitis in primary care centres and the direct and comprehensive cost-effectiveness of four alternative strategies for the management of group A streptococcal pharyngitis and the prevention of rheumatic fever were assessed in a 1-year prospective randomized study, carried out in children between the ages of 5 and 14 years. Data from the study showed that the test was easy to perform and reliable when introduced as a service in primary care. The strategy of using the rapid antigen detecting test and a 10-day oral penicillin course for diagnosis and treatment proved to be the safest and most cost-effective. If compliance with a 10-day course of oral penicillin is unlikely to be achieved, the strategy of introducing the test and treatment by intramuscular benzathin penicillin G proved to be the second best cost-effective alternative. In developing countries, where acute rheumatic fever is still common and the cost of the test and a 10-day course of penicillin may prove to be formidable, a strategy of treating all children with pharyngitis with intramuscular benzathin penicillin G seems to be the most cost-effective. The strategy of diagnosing group A streptococcal pharyngitis on clinical grounds proved to be the worst.

Preparation, assessment and preservation of antigen from Brucella abortus strain 45/20 for use in the rough antigen complement fixation test.

Two methods of extraction were used to prepare antigens from Brucella abortus rough strain 45/20. The antigens were assessed for use in the complement fixation test. A suitable antigen was prepared using the saline extraction method of Miller et al. (1976) and used extensively in CF tests. Four methods of preservation were compared; -20 degrees C, -196 degrees C, 0.5% phenol at 4 degrees C, and lyophilisation. The antigen could be stored at -20 degrees C or -196 degrees C for up to 2 years.

Assessment of Dharmendra antigen. II. Standardisation of the antigens.

Dharmendra antigen with different bacterial counts (16, 12.5, 10, 7.5, 5 and 2.5 million/ml) have been utilized for determination of skin delayed hypersensitivity in leprosy patients. It has been noted that antigen with 10 million acid fast bacilli (AFB)/ml mounts a standard early (24 hrs) as well as late (3 weeks) reaction in patients. Lepromatous patients do not show any skin reaction with this dilution. Thus, a standard Dharmendra antigen has been prepared using a considerably smaller number of organisms as compared to the International standards for Mitsuda antigen.

Assessment of Dharmendra antigen. III. Comparative study with Mitsuda antigen.

Four fractions each from Dharmendra and Mitsuda antigen have been obtained by step-wise centrifugation and sonication of the antigen. These fractions have been assessed for their capacity of inducing skin delayed hypersensitivity response. While, it has been noted that all fractions of both types of antigens can induce a good early reaction, the late skin reaction is only mounted by intact bacilli of both types of antigen. When compared at a constant bacillary concentration, Dharmendra antigen has produced better early skin reaction than Mitsuda antigen, whereas the intensity of late skin reaction is almost equal with both the antigens. The hypothesis has been put forward that the early, as well as the late reaction are produced by the same antigen and this antigen is located in the protoplasm of M. leprae.