Comparison of the detection of Helicobacter pylori infection by commercially available serological testing kits and the 13C-urea breath test.

BACKGROUND: Serum Helicobacter pylori (H. pylori) antibody kits (LZ and LIA) using the latex agglutination immunoassay method are commercially available, but few studies have been performed to determine their diagnostic accuracy or to compare their results with those of enzyme-linked immunosorbent assay (ELISA) kits (EP and EIA). METHODS: Sera were obtained from 213 hospital outpatients with dyspeptic symptoms. The serological results were compared with the result of the 13C-urea breath test (UBT) which seems to be reliable. RESULTS: Of the 213 subjects, 154 were diagnosed as positive for H. pylori infection according to the UBT. The sensitivities and specificities of these tests were 97.4% and 76.3%, 98.1% and 78.0%, 99.4% and 74.6%, and 98.1% and 71.2% for the EP, LZ, EIA and LIA tests, respectively. When the 13 subjects whose seropositive results of the four kits were completely opposite to the negative results of the UBT were excluded, the specificities of evaluated kits were all higher than 90%. The concordance rate between the EP and EIA tests was 98.1% (Spearman's rank correlation coefficient = 0.83) and that between the LZ and LIA tests was 97.1% (correlation coefficient = 0.91). The LZ gave higher antibody titer value than EP (p < 0.0001, Z = 9.82; Wilcoxon signed-rank test), and EIA gave higher value than LIA (p < 0.0001, Z = 6.43; Wilcoxon signed-rank test). CONCLUSIONS: The latex immunoassay method provided the same reliability to ELISA in terms of the diagnostic accuracy for current H. pylori infection, although we should take into account the titer value differences by each test method in practical use.

Development and evaluation of a latex agglutination test for the rapid serodiagnosis of tularemia.

A latex agglutination test (LAT) was developed for a rapid detection of antibodies against Francisella tularensis. The assay is performed by mixing serum with antigen-coated latex beads and read within 5 min. Developed LAT has been proved to be a specific, sensitive, fast, easy-to-perform and cost-efficient tool for the routine diagnosis of tularemia.

Development of a simple and rapid method for the specific identification of organism causing anthrax by slide latex agglutination.

UNLABELLED: A specific latex agglutination test (LAT) based on anti-PA (protective antigen) antibodies having detection limit of 5 × 10(4) formalin treated Bacillus anthracis cells or 110 ng of PA was optimized in this study. The optimized LAT could detect anthrax toxin in whole blood as well as in serum from the animal models of anthrax infection. The protocol is a simple and promising method for the specific detection of bacteria causing anthrax under routine laboratory, as well as in field, conditions without any special equipments or expertise. SIGNIFICANCE AND IMPACT OF THE STUDY: The article presents the first report of a latex agglutination test for the specific identification of the cultures of bacteria causing anthrax. As the test is targeting one of anthrax toxic protein (PA), this can also be used to determine virulence of suspected organisms. At the same time, the same LAT can be used directly on whole blood or sera samples under field conditions for the specific diagnosis of anthrax.

'Leptorapide' - a one-step assay for rapid diagnosis of human leptospirosis.

SUMMARY: Leptospirosis is a globally important zoonotic infection caused by spirochaetes of the genus Leptospira. It is transmitted to humans by direct contact with infected animals or indirectly via contaminated water. It is mainly a problem of the resource-poor developing countries of the tropical and sub-tropical regions of the world but outbreaks due to an increase in travel and recreational activities have been reported in developed and more industrialized areas of the world. Current methods of diagnosis are costly, time-consuming and require the use of specialized laboratory equipment and personnel. The purpose of this paper is to report the validation of the 'Leptorapide®' test (Linnodee Ltd, Northern Ireland) for the diagnosis of human leptospirosis. It is a simple one-step latex agglutination assay performed using equal volumes of serum sample and antigen-bound latex beads. Evidence of leptospiral antibodies is determined within minutes. Agglutination is scored on a scale of 1-5 and the results interpreted using a score card provided with the kit. Validation has been performed with a large sample size obtained from individuals originating from various parts of the world including Brazil and India. The test has shown sensitivity and specificity values of 97·1% and 94·0%, respectively, relative to the microscopic agglutination test. The results demonstrate that Leptorapide offers a cost-effective and accurate alternative to the more historical methods of antibody detection.

A cost-effective protocol for screening patients for methicillin-resistant Staphylococcus aureus.

The incidence of hospital-acquired infection with methicillin-resistant Staphylococcus aureus (MRSA) is rising worldwide. Rapid identification of MRSA carriers is an important step in reducing the risk of transmission to other patients. Molecular methods are increasingly popular but are technically demanding and expensive. This study assesses the modification of one of the commercially available latex agglutination tests (Mastalex-MRSA) for the identification of penicillin-binding protein 2' on known strains of MRSA as well as other organisms identified from chromogenic agar plates. A total of 3050 patients with unknown MRSA status were processed through the routine laboratory during the investigation period and 73 of these were presumptive positive following overnight incubation. Of 70 patients who could be evaluated, 32 (43.8%) specimens would be suitable for use with the kit directly from overnight incubation on chromogenic agar, and the other 38 (52.1%) would be suitable following four hours' incubation on blood agar. The cost of one positive MRSA test with the inclusion of this test is Euro 15.15 compared with published reports of Euro 35.00 for a commercial polymerase chain reaction (PCR) test. This protocol would allow the reporting of presumptive positive MRSA results approximately 24 hours earlier than currently achieved.

Rapid serodiagnosis of leptospirosis by latex agglutination test and flow-through assay.

PURPOSE: Diagnosis of leptospirosis facilitates patient management and initiation of therapy. The microscopic agglutination test (MAT) is the serological test used in reference laboratories because of its high degree of sensitivity and specificity. But the results are not available quickly for patient management. In the present study, in order to develop a simple, rapid immunodiagnostic assay, one of the outer membrane proteins (OMPs), recombinant LipL41 (rLipL41) has been utilised in latex agglutination test (LAT) and flow-through assay. METHODS: Part of LipL41 gene was expressed in Escherichia coli system and purified. The rLipL41 antigen of pathogenic Leptospira interrogans serovar Icterohaemorrhagiae, which is conserved in all pathogenic Leptospira spp. was used as capture antigen in the LAT and flow-through test. Both tests are very rapid and could be completed within 5 minutes. The sensitivity and specificity of rLipL41 was assessed and evaluated in LAT and flow-through assay in comparison with standard MAT. RESULTS: The sensitivity and specificity of the LAT were 89.70 and 90.45% and flow-through assay were 89.09 and 77.70%, respectively. CONCLUSIONS: The developed LAT and flow-through assays were simple, rapid and economical for the detection of leptospira infection and suitable for large-scale screening of samples in endemic areas without any sophisticated equipment.

Evaluation of methods and costs for detecting methicillin-resistant Staphylococcus aureus isolates from clinical specimens at regional hospitals in Trinidad and Tobago / Evaluación de métodos y costos para la detección de aislados de Staphylococcus aureus resistentes a la meticilina a partir de especímenes clínicos en los hospitales regionales de Trinidad y Tobago

OBJECTIVES: To evaluate and determine the most cost effective, rapid and specific method for detection of methicillin resistance in clinical isolates of S aureus in a setting with limited personnel and resources. METHODS: Standard laboratory methods were used to identify S aureus isolates. The conventional Methicillin Resistance Staphylococcus aureus (MRSA) detection methods used included, 1 µg oxacillin disk diffusion, oxacillin salt agar screen (CLSI), penicillin binding protein (PBP 2') latex agglutination test and E-tests oxacillin. Results of conventional tests were compared with a polymerase chain reaction (PCR) method for detecting MRSA isolates. Polymerase chain reaction detection of the mecA gene in S aureus was used as the " gold standard" for MRSA identification. RESULTS: All methods had 100% sensitivity except for oxacillin disk diffusion and oxacillin-salt agar screening with 98% and 99%, respectively. Specificity was also 100% for all methods except for oxacillin-disk diffusion (99%). Turn around time (TAT) for detection of MRSA was calculated to be within six hours for PCR. The fastest TAT of 1.25 hours was obtained for PBP 2' latex agglutination. Total cost for labour and materials to perform each method was highest for E-test, US$13.76/isolate. The cost for PCR when compared to that of latex agglutination was not statistically significant (US$3.74 vs US5.91, p = 0.4). CONCLUSIONS: All methods presented high sensitivity and specificity, but the latex agglutination test had the advantage of giving a reliable, rapid and most cost effective result that compares well to PCR in this environment.

OBJETIVOS: Evaluar y determinar el método más específico, rápido y costo-efectivo para la detección de la resistencia a la meticilina en aislados clínicos de S aureus en un lugar con personal y recursos limitados. MÉTODOS: A fin de identificar los aislados de S aureus, se utilizaron métodos estándar de laboratorio. Los métodos convencionales de detección de SARM usados incluyeron difusión por disco de oxacilina de 1 µg, prueba de tamizaje (" screening" ) de oxacilina en agar-sal (CLSI), test de aglutinación en látex para la detección de la proteína 2 fijadora de la penicilina (PBP 2'), y la prueba E-Test de oxacilina. Los resultados de las pruebas convencionales fueron comparados con un método de PCR para la detección de aislados SARM. La detección por PCR del gene mecA en S aureus fue usada como " estándar de oro" para la identificación de SARM. RESULTADOS: Todos los métodos tuvieron 100% de sensibilidad excepto la difusión por disco de oxacilina y el tamizaje de oxacilina en agar-sal, con 98% y 99% respectivamente. La especificad también fue de 100% para todos los métodos, con excepción de la difusión por disco de oxacilina (99%). El tiempo de respuesta (TAT, del inglés turn around time) para la detección de SARM se halla, según los cálculos, dentro de las seis horas para PCR. El TAT más rápido, 1.25 hrs, se obtuvo en la aglutinación en látex de PBP 2'. El costo total del trabajo y los materiales en la ejecución de cada método fue más alto en la prueba de E-Test, aislado/$13.76 USD. El costo de PCR en comparación con el de la aglutinación látex no fue estadísticamente significativo ($3.74 USD vs $5.91USD, p = 0.4). CONCLUSIONES: Todos los métodos presentaron alta sensibilidad y especificidad, pero el test de aglutinación en látex tuvo como ventaja el ofrecer un resultado confiable, rápido y altamente costo-efectivo, no muy diferente del PCR en este ambiente.

Evaluation of methods and costs for detecting methicillin-resistant Staphylococcus aureus isolates from clinical specimens at regional hospitals in Trinidad and Tobago.

OBJECTIVES: To evaluate and determine the most cost effective, rapid and specific method for detection of methicillin resistance in clinical isolates of S. aureus in a setting with limited personnel and resources. METHODS: Standard laboratory methods were used to identify S. aureus isolates. The conventional Methicillin Resistance Staphylococcus aureus (MRSA) detection methods used included, 1 microg oxacillin disk diffusion, oxacillin salt agar screen (CLSI), penicillin binding protein (PBP 2') latex agglutination test and E-tests oxacillin. Results of conventional tests were compared with a polymerase chain reaction (PCR) method for detecting MRSA isolates. Polymerase chain reaction detection of the mecA gene in S. aureus was used as the "gold standard" for MRSA identification. RESULTS: All methods had 100% sensitivity except for oxacillin disk diffusion and oxacillin-salt agar screening with 98% and 99%, respectively. Specificity was also 100% for all methods except for oxacillin-disk diffusion (99%). Turn around time (TAT) for detection of MRSA was calculated to be within six hours for PCR. The fastest TAT of 1.25 hours was obtained for PBP 2' latex agglutination. Total cost for labour and materials to perform each method was highest for E-test, US$13.76/isolate. The cost for PCR when compared to that of latex agglutination was not statistically significant (US$3.74 vs US5.91, p = 0.4). CONCLUSIONS: All methods presented high sensitivity and specificity, but the latex agglutination test had the advantage of giving a reliable, rapid and most cost effective result that compares well to PCR in this environment.

Biological diagnosis of meningococcal meningitis in the African meningitis belt: current epidemic strategy and new perspectives.

Laboratory diagnosis is an essential component in surveillance of meningococcal epidemics, as it can inform decision-makers of the Neisseria meningitidis serogroup(s) involved and the most appropriate vaccine to be selected for mass vaccination. However, countries most affected face real limitations in laboratory diagnostics, due to lack of resources. We describe current diagnostic tools and examine their cost-effectiveness for use in an epidemic context. The conclusion is that current WHO recommendations to use only the latex agglutination assay (Pastorex) at epidemic onset is cost-effective, but recently developed rapid diagnostic tests for the major epidemic-causing meningococcal serogroups may prove a breakthrough for the future.

Evaluation of serodiagnostic tests for T.b. gambiense human African trypanosomiasis in southern Sudan.

A survey was conducted in a low-endemic and in a non-endemic area of Sudan to evaluate the specificity and efficiency of different serological antibody detection techniques for Trypanosoma brucei gambiense. Comparisons were made of the card agglutination test for trypanosomiasis (CATT) on diluted blood, on diluted plasma and on eluates from blood dried on filter paper, the LATEX test on diluted plasma and an ELISA on diluted plasma and filter paper. The specificities of all the serological tests were not significantly different from CATT on diluted blood (99.5%). The specificity of CATT on diluted blood was similar (99.3%). The highest sensitivities (100%) were observed with CATT on diluted blood and with CATT and LATEX on diluted plasma. CATT on diluted blood was more cost-efficient than the classic test, CATT on whole blood.

More laboratory testing: greater cost but not necessarily better.

BACKGROUND: The bacterial latex agglutination assay is ordered predominantly on the pediatric population, for rapid screening for bacterial surface antigens in cerebrospinal fluid (CSF) or urine specimens. The high cost of this assay and questions raised in the literature regarding its accuracy led to a retrospective review of the use of this assay at a medium-sized midwest teaching hospital. The results of 6,370 bacterial latex agglutination tests performed between May, 1995, and November, 1996, and charts of patients being tested were reviewed. RESULTS: This study demonstrated a sensitivity and specificity of 28.6% and 86.7% for urine specimens and 70.0% and 99.4% for CSF specimens. A total of 11 pathogens were accurately detected (7 CSF and 4 urine). There were 13 false negatives and 59 false positives. None of the true positives had a discernible effect on either treatment or hospital course; however, several of the erroneous tests resulted in delayed or unnecessary treatment and workup of the involved patients. The annual billed cost of this test at this institution (fiscal years 1995 to 1997) averaged $167,000 per annum. This does not include indirect costs associated with increased length of hospital stay, overutilization of antibiotics and excess laboratory tests ordered as a result of false positives. CONCLUSIONS: Bacterial antigen latex agglutination testing is neither sufficiently sensitive nor specific to be used as a screening test. Accurate results have no demonstrable clinical impact, whereas numerous inaccurate results are often generated at great cost. The continued use of the latex agglutination assay should be seriously questioned in an era when cost containment and clinical efficiency are becoming increasingly important.

Seroconversion rates in healthcare workers using a latex agglutination assay after varicella virus vaccination.

OBJECTIVES: To determine the seroconversion rate after varicella immunization of healthcare workers (HCWs) and the effect of seroconversion rate on current cost-based recommendations for universal vaccination. METHODS: A voluntary vaccination program for HCWs was performed at a tertiary-care cancer center in New York City. A commercial latex agglutination assay was used to test postvaccination antibody response. Costs for vaccination and postvaccination serological testing were compared to potential costs of postexposure employee furloughs. RESULTS: Of 263 seronegative HCWs, 96 (36.5%) began the vaccine program. Thirty-nine HCWs received only one dose of vaccine. Seven returned for follow-up antibody testing, of whom 4 were seropositive. Of the 57 HCWs who received two doses, 38 returned for follow-up serology. Thirty-one (81.6%) HCWs were seropositive for varicella-zoster virus antibodies, and seven HCWs (18.4%) remained seronegative. Total cost of vaccination for all 263 seronegative HCWs was estimated and compared to the cost of varicella-related furloughs at our institution. CONCLUSIONS: We found a considerably lower rate of vaccine-induced seroconversion at our hospital compared to that of the published literature. Despite this finding, universal varicella vaccination remained an extremely cost-effective alternative to the furloughing of exposed, seronegative HCWs. Projected hospital savings exceeded $53,000 in the first year after vaccination alone.

Comparison between RT-PCR and rapid agglutination test for diagnosis of human rotavirus infection.

Rotavirus represents the major cause of dehydrating diarrhea among infants and young children on worldwide scale and has recently become the target of research aimed at developing a vaccine. To that end, screening tests of clinical specimens ought to provide high sensitivity and specificity. Hence, in order to achieve that aim we compared a commercially available latex agglutination (LA) kit with reverse transcription polymerase chain reaction (RT-PCR) using primers amplifying the gene for the major neutralization antigen in 71 stool samples of children with acute gastroenteritis during November 1998-April 1999. Based on accuracy (76.05%), specificity (86.8%) and sensitivity (63.6%) determined for LA with RT-PCR serving as the gold standard, we recommend LA for field studies where speed and simplicity are crucial. Yet, for the purpose of further studies as to epidemiology and vaccine trials RT-PCR with its higher specificity and sensitivity will be required.

Evaluation of a rapid enzyme immunoassay for diagnosis of hepatic amoebiasis.

We compared the capability of rapid enzyme immunoassay (EIA) to detect antiamoebic antibodies during hepatic amoebiasis with those of indirect hemagglutination and latex agglutination. EIA is simple to perform and rapid (20 min) and does not require any special equipment (optical reading is sufficient). EIA of 143 sera (including 43 from patients with proven hepatic amoebic abscess, 33 from patients with other hepatic disorders and/or parasitic infections, and 67 from healthy individuals) yielded a specificity, a sensitivity, and positive and negative predictive values of 100, 93, 100, and 97.1, respectively. This test could thus be considered another valuable tool for the diagnosis of hepatic amoebiasis.

The fat emulsion agglutination test: a reliable and cost effective alternative to the latex agglutination test for rapid bedside CRP measurement.

We compared two tests for bedside C reactive protein (CRP) measurement: the latex agglutination test (LAT) and the fat agglutination test (FAT). FAT is based on the property of CRP to agglutinate fat emulsions in the presence of CaCl2. The sensitivity, specificity and accuracy of FAT and LAT to detect a CRP > 10 mg/l, determined with radial immunodiffusion (n = 500 pediatric patients, CRP range 0- > 80 mg/l), were 91%, 82% and 90% respectively for FAT and 82%, 95% and 85% for LAT. FAT reagent could be stabilized with NaN3 (0.02%) for at least one year, when stored at 4 degrees C (n = 49). NaN3 (0.02%) had no effect on agglutination of FAT (n = 40). In conclusion, in pediatric patients, FAT is a reliable and cost effective alternative to LAT, if serum samples are used.

The effect of a rapid kit for detection of streptococcal pharyngitis on the accuracy of the physicians' diagnoses.

BACKGROUND: In the last decade, the accuracy of rapid tests for detection of group A streptococcal antigen was evaluated in laboratory and clinical settings, and the tests were suggested as an alternative to the traditional throat culture. METHODS: We evaluated 19 patients with a preliminary diagnosis of nonstreptococcal pharyngitis and 13 patients with a preliminary diagnosis of streptococcal pharyngitis. The physician performed a rapid latex agglutination test (Detect A Strep), took throat culture from all of the patients, reconsidered the preliminary diagnosis, and made a working diagnosis. A clinical score was calculated for each patient during data analysis. The accuracy of the physicians' preliminary diagnoses was compared with the accuracy of the scoring system, with the accuracy of the latex agglutination test, and with the accuracy of the physicians' working diagnoses. RESULTS: The scoring system, the physicians' preliminary diagnoses, the latex agglutination test, and the physicians' working diagnoses correlated significantly with throat culture results (p < or = 0.05). The efficiency of the physicians' preliminary diagnoses was 75% compared with an efficiency of 69% of the clinical scoring system, an efficiency of 66% of the latex agglutination test, and an efficiency of 69% of the physicians' working diagnoses. The physician changed the preliminary diagnosis only for two patients as a result of the latex agglutination test results; ironically, however, the preliminary diagnosis was correct in both of these cases. CONCLUSION: The use of a rapid test for the diagnosis of group A streptococcal antigen under normal working conditions did not improve the accuracy of the physician's diagnosis, so the use of the latex agglutination test in this study was not cost-effective.

To culture or not to culture: fecal lactoferrin screening for inflammatory bacterial diarrhea.

Because of its low yield in unselected specimens, stool culture is often cost ineffective. We tested 55 fecal samples from Fairfax Hospital (46 patients with diarrhea and 9 from controls without diarrhea) for lactoferrin by latex agglutination (LFLA) with the Leukotest (Techlab, Blacksburg, Va.) as a marker for inflammatory diarrhea. Of the 28 samples with Salmonella, Shigella, or Campylobacter infection, 93% had detectable fecal lactoferrin at > or = 1:50 (61% had LFLA titers of > or = 1:400), while 83% of 18 samples with rotavirus or no detectable pathogen were LFLA negative at a titer of 1:50 (100% were negative at 1:400). All 9 controls without diarrhea were LFLA negative at 1:50. The use of fecal lactoferrin to screen for inflammatory diarrhea selects specimens for which stool culture is fivefold more likely to yield an invasive bacterial pathogen (reducing the cost per positive result by over $800) and thus may greatly enhance a cost-effective approach to evaluating diarrheal illness.

Quality assurance study of bacterial antigen testing of cerebrospinal fluid.

Bacterial antigen testing (BAT) of cerebrospinal fluid (CSF) by latex agglutination is a low-yield procedure in patients whose CSF specimens have normal laboratory parameters. Between August 1992 and August 1994, we evaluated 287 bacterial antigen (BA) test requests to determine whether yields could be improved and whether patient costs could be reduced by cancelling BAT for those patients with normal CSF parameters (cell count, protein, glucose) after consultation with physicians. A total of 171 (68%) BA tests were canceled by this approach. None of these CSF specimens was culture positive for an organism detectable by BAT. Of the remaining 116 CSF specimens tested, only 3 were positive by BAT, one each for Neisseria meningitidis, Streptococcus pneumoniae, and group B streptococcus. Only 43 of the CSF specimens tested had at least two abnormal parameters; the 3 positive CSF specimens were included in this group. In light of the low rate of positivity, the number of BA tests can be further reduced by establishing criteria that must be met before a CSF specimen is accepted for BAT. After review of our data and the literature concerning this topic, we concluded that only specimens with leukocyte counts of > or = 50 cells per mm3 should be tested. Of 287 specimens evaluated in our study, only 36 met this criterion, including the 3 BA-positive specimens. Enacting such a restriction would have reduced the total number of BA tests by 251 (87%) without compromising patient care. A laboratory cost savings of $6,500 per year would have been realized, with a substantial reduction in the cost per positive test. Patient charges would have been reduced by $12,500 per year.

Latex particle agglutination tests on the cerebrospinal fluid. A reappraisal.

Rapid diagnostic tests are often used to identify microbial etiology of infection early. Latex particle agglutination (LPA) tests on the cerebrospinal fluid (CSF) are frequently used for purpose of rapid diagnosis. We evaluated their usefulness in management of patients with suspected meningitis. We also evaluated the cost effectiveness of LPAs during an 11-month period; 1,540 CSF specimens were tested for H. influenzae type b, Group B streptococcal (GBS), N. meningitidis and S. pneumoniae using LPAs. Only 27 were positive. LPAs were useful in management of only the neonates with GBS infection. On the whole, LPAs were very expensive and not cost-effective.