Optical Immunoassay Research Articles

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

To perform a cost-effectiveness analysis of treatment management strategies for children older than 3 years who present with signs or symptoms of pharyngitis. 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. 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. In a setting with adherent patients, children with sore throats should generally get throat cultures in lieu of rapid streptococcus antigen tests.

Fixed-polarizer ellipsometry: a simple technique to measure the thickness of very thin films

The fixed-polarizer ellipsometer measures thickness of thin films. It is simple, inexpensive, and provides a linear response over a range of 800 A. We develop a matrix formulation to describe the optical characteristics of the instrument and apply it to the case of a single thin film on a substrate. Excellent agreement is found between experimental and simulated results. Applying the instrument to optical immunoassay, we show that its sensitivity can extend to 4 pg/ml, depending upon the analyte. This compares favorably with commercially available manual and automated immunoassay systems. The fixed-polarizer ellipsometer appears to be well-suited for use in laboratory and production environ- ments. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)02205-9)

Evaluation of the Strep B OIA Test Compared to Standard Culture Methods for Detection of Group B Streptococci

Objective:This study evaluated the accuracy of the commercial product Strep B OIA (optical immunoassay) compared to the standard agar and broth culture methods for detecting vaginal colonization with group B streptococcus (GBS).Methods:Preoperative vaginal cultures were obtained from 141 nonpregnant gynecological patients undergoing major gynecologic surgery. Major gynecologic surgery was defined as benign gynecologic, gyne-oncology, and urogynecologic procedures. The results of the Strep B OIA test were compared to the results obtained from SXT agar (selective for GBS), colistin-nalidixic acid (CNA) agar, and Todd-Hewitt broth cultures.Results:The prevalence of vaginal GBS colonization in this population was 20.6%. The sample sensitivity and specificity of the OIA method were 58.6% and 85.7%, respectively. These values are lower than the sensitivity and specificity of 85.4% and 91.5%, respectively, given in the OIA package insert. Although the sample negative predictive value was fairly high (88.9%), the positive predictive value was low (51.5%).Conclusion:Although a previous study stated that the product Strep B OIA reduces the time required to obtain results (30 minutes versus days) and can, therefore, function as a useful diagnostic tool in the management of early-onset GBS disease, the present study's finding of low sensitivity and low positive predictive value indicates that this test may have very limited clinical value. Infect. Dis. Obstet. Gynecol. 7:202–205, 1999.

Evaluation of an optical immunoassay test for rapid detection of influenza A and B viral antigen

An optical immunoassay test, FLU OIA (BIOSTAR, USA), was evaluated for the diagnosis of influenza viral infection. The reactivity of the FLU OIA test was evaluated using 42 influenza strains (25 human influenza A, 12 human influenza B, 2 swine influenza A and 3 avian influenza A strains). The FLU OIA test showed positive results for all influenza strains. There was no evidence that cross-reactivity occurred with non-influenza viruses. The detection limit of the FLU OIA test was found to be 3.0-6.5 x 10(4) pfu/assay for human influenza A and B strains. The sensitivity and specificity of the FLU OIA test compared to isolation in cell culture was 89.7% and 76.0% for testing of 54 nasopharyngeal aspirate specimens. The FLU OIA test is rapid and easy for the detection of influenza A and B viral antigen and provide a valuable tool for the rapid diagnosis of influenza viral infection.

Evaluation of a new rapid antigen detection kit for group A beta-hemolytic streptococci.

To evaluate the use of a new rapid antigen-detection kit for group A beta-hemolytic streptococcus and compare results with previously published studies. Throat swabs were obtained prospectively from patients, aged one to 18 years, presenting to the emergency department, acute concerns clinic, and walk-in clinic of an urban tertiary care children's hospital. Throat swabs were first inoculated on a 5% sheep blood agar plate and then used for the streptococcus A optical immunoassay (OIA) kit. Results of both the throat culture and the rapid antigen-detection test were then compared. Two-hundred thirty-three patients were enrolled. Seventy-three patients had a positive culture and 63 patients had a positive OIA. Fifteen patients had a false negative result for the OIA kit and five patients had a false positive result. Test sensitivity was 79.5%, specificity was 96.9%, positive predictive value was 92.1%, and negative predictive value was 91.2% Although previous studies have demonstrated OIA kit sensitivities as high as 98.9% and authors have, as a result, recommended that the performance of a backup throat culture for a negative OIA test is unnecessary, our results do not support this. A sensitivity of 79.5% is not sufficiently high to justify omission of a standard throat culture. Accordingly, all OIA tests that are negative should be confirmed by the performance of a throat culture.

Cost-Effectiveness of Chlamydial Screening

Cost-Effectiveness of Chlamydial Screening

Rapid detection of group A streptococcal antigen with a new optical immunoassay.

Rapid detection of group A streptococcal antigen with a new optical immunoassay.

Detection of group B streptococcus: Comparison of an optical immunoassay with direct plating and broth-enhanced culture methods

Detection of group B streptococcus: Comparison of an optical immunoassay with direct plating and broth-enhanced culture methods

A comparison of the BioStar Strep A OIA™ rapid antigen assay, Group A Selective Strep Agar (ssA™), and Todd-Hewitt broth cultures for the detection of group A Streptococcus in an outpatient Family Practice setting

In some studies the BioStar™ Strep A OIA (optical immunoassay) has yielded inconsistent results, although originally it was reported to be more sensitive than conventional culture for the detection of group A Streptococcus (GAS). The Group A Selective Strep Agar with 5% sheep blood (ssA™) incubated anaerobically has been reported to be more sensitive than conventional culture in the detection of GAS. We compared the BioStar™ Strep A OIA GAS rapid antigen detection kit to anaerobic culture on ssA™ with and without preincubation in Todd-Hewitt broth (THB) for the detection of GAS. From September 1995 through January 1996, throat swabs were collected in duplicate from 75 children (≤18 years) and 188 adults (>18 years) who presented with pharyngitis in the outpatient University of New Mexico Family Practice Clinic. Thirty-one (12%) of the 263 cases were positive for GAS by culture and/or broth. Compared with anaerobic culture on the ssA™, with and without preincubation in THB, the sensitivity, specificity, positive predictive value, and negative predictive value of the BioStar™ Strep A OIA were 77, 62, 22, and 95%, respectively. Compared with enrichment in THB followed by subculture on ssA™ and anaerobic incubation, the sensitivity, specificity, positive predictive value, and negative predictive value of direct culture on ssA™ and anaerobic incubation were 79, 99, 98, and 96%, respectively. All isolates were serologically grouped. The BioStar™ Strep A OIA is as sensitive as direct culture on ssA™ incubated anaerobically, but the low specificity and low positive predictive value when the OIA is used in low prevalence populations could lead to unnecessary antibiotic treatment.

Polymerase chain reaction for Streptococcus pyogenes used to evaluate an optical immunoassay for the detection of group A streptococci in children with pharyngitis.

In evaluations of sensitive rapid tests for group A streptococci such as the optical immunoassay (OIA), some samples are positive by the antigen test but negative by culture. A method is needed for resolving these discrepant results. To develop a PCR-based assay to detect group A streptococci and to use it to establish a reference standard for evaluating an OIA for group A streptococcal antigen. A PCR assay that detects a segment of the MF gene of Streptococcus pyogenes was developed for the detection of group A streptococci in throat swabs. Paired swabs were obtained from 200 children with symptomatic pharyngitis and used to perform OIA, agar culture, broth-enhanced culture and PCR. As a reference standard any patient with group A streptococci detected by either culture or PCR was considered to be truly positive. In comparison to agar and broth-enhanced culture procedures, OIA had sensitivities of 82 and 80% and specificities of 87 and 89%, respectively. Eight (44%) of 18 samples that were positive by OIA but negative by culture were positive for group A streptococci by PCR. Compared with the reference standard, sensitivities were OIA 76%, agar culture 79%, broth-enhanced culture 86% and PCR 96%. The specificity of OIA was 92%. PCR can be used to establish a reference standard for evaluating rapid tests for group A streptococci. With this reference standard OIA was nearly as sensitive as but less specific than agar culture for detection of group A streptococci. Maximum detection requires use of both tests.

Use of Optical Immunoassay to Diagnose Streptococcal Pharyngitis

<h3>To the Editor.</h3> —In the article by Dr Gerber and colleagues¹reporting an office-based multicenter investigation of the optical immunoassay (OIA) test for group A β-hemolytic streptococcal (GABHS) pharyngitis, the authors concluded that "with adequately trained personnel, negative OIA test results may not always need to be routinely confirmed with blood agar plate (BAP) cultures." We believe the authors' conclusions are based less on the quality of the testing personnel or the performance specifications of the OIA and more on the quality of the BAP culture procedure used in the study. Presumptive differentiation of GABHS and non—group A streptococci may be accomplished by the bacitracin test, in which a zone of inhibition is noted on a pure subculture of β-hemolytic colonies. Bacitracin disks placed on primary cultures on nonselective media, as was done in this study, may detect as little as 54% of group A streptococci.²We compared

Optical Immunoassay Test for Group A β-Hemolytic Streptococcal Pharyngitis

To compare the accuracy of an optical immunoassay (OIA) for the rapid diagnosis of group A streptococcal pharyngitis with blood agar plate (BAP) culture. Blinded comparison with criterion standard. A total of 6 private pediatricians' offices, 3 in Connecticut and 3 in Chicago, III. A total of 2113 consecutive patients with acute pharyngitis, 983 in Connecticut and 1130 in Chicago. The sensitivities and specificities of OIA and BAP culture (both performed and interpreted in the office) were determined using a research laboratory's interpretation of a combination of BAP culture and Todd-Hewitt broth (THB) culture of transport tube pledget as criterion standard. Among patients in Connecticut, the sensitivities of the OIA and BAP culture were 94% and 89%, respectively (P=.004), while the specificities were 96% and 99%, respectively (P=.001). Among patients in Chicago, the sensitivities of the OIA and BAP culture were 79% and 72%, respectively (P<.001), while the specificities were 89% and 99%, respectively (P<.001). In each of the 6 pediatricians' offices, the OIA was more sensitive than the BAP culture. Combining the data from Connecticut and Chicago, the overall sensitivities of the OIA and BAP culture were 84% and 78%, respectively (P<.001), while the specificities were 93% and 99%, respectively (P<.001). The results of this comprehensive office-based investigation suggest that with adequately trained personnel, negative OIA test results may not always need to be routinely confirmed with BAP cultures.

Detection of group B streptococcus by optical immunoassay and direct agar plate culture: Comparison to broth enhanced culture

Detection of group B streptococcus by optical immunoassay and direct agar plate culture: Comparison to broth enhanced culture

Inadequacy of rapid immunoassays for intrapartum detection of group B streptococcal carriers

To determine the accuracy of two currently used immunoassays and a newly developed optical immunoassay for rapid intrapartum detection of group B streptococcal colonization compared with culture methods. Rayon-tipped swabs were used to collect specimens from the distal vagina of 502 women at admission for labor or rupture of membranes. Four tests were performed on specimens from the first 197 patients: culture in selective broth medium, semiquantitative culture on blood agar medium, and ICON Strep B and Quidel Group B Strep Test enzyme immunoassays. For the remaining 305 women, a fifth test, Strep B OIA, a newly developed optical immunoassay, was also performed. The prevalence of group B streptococcal vaginal colonization was 25.1% by selective broth medium and 17.3% when swabs were plated directly onto blood agar medium, giving the latter method a sensitivity of 69%. When compared with selective broth medium results, the sensitivities of the rapid immunoassays were 12% (Quidel), 15% (ICON), and 37% (Strep B OIA). These values rose to 16% (Quidel), 21% (ICON), and 53% (Strep B OIA) when compared with nonselective blood agar medium results. For women with heavy group B streptococcal colonization (more than 10(6) colony forming units/mL), the sensitivities were 36% (Quidel), 46% (ICON), and 100% (Strep B OIA). Specificities for all assays were high (98-100%), but variability was found in positive (79-100%) and negative (77-85%) predictive values. Although Strep B OIA reliably detects women with heavy group B streptococcal colonization and is more sensitive than either the ICON or Quidel enzyme immunoassays, none of these rapid assays is sufficiently accurate for routine use in the intrapartum detection of women colonized with group B streptococcus.

Rapid detection of group B streptococcal antigen from vaginal specimens using a new Optical ImmunoAssay technique

A total of 531 vaginal specimens were used to evaluate a new Optical ImmunoAssay (OIA) screening technique for the rapid detection of group B streptococcal antigen. The results of the OIA test, the ICON Strep B membrane immunoassay (Hybritech ICON), and conventional culture on sheep blood agar (direct TSA) were compared to broth enhanced culture. Results obtained from the OIA test, ICON, and direct TSA yielded 72, 39, and 68 positives, respectively, as compared to 100 positives using the Lim broth culture method as the standard. The Optical ImmunoAssay technique is as sensitive as the conventional plating method and is capable of providing results in 30 minutes.

Optical immunoassay for rapid detection of group A beta-hemolytic streptococci. Should culture be replaced?

To evaluate an optical immunoassay rapid antigen test to detect group A beta-hemolytic streptococci directly from throat swab specimens. Criterion standard with "blinded" comparison. Double-swab pharyngeal samples were obtained; one swab was cultured and the other was used for the rapid antigen test. Microbiology laboratory in a primary care center at a university teaching hospital. Two hundred sixty-two outpatients with pharyngitis. The results of the optical immunoassay rapid antigen test were compared with results of standard aerobic culture. Sixty-two (24%) of 262 samples were culture-positive; 48 of these 62 were positive by the optical immunoassay rapid test (sensitivity, 77%). Of the 200 culture-negative samples, seven (4%) were positive by the rapid test (specificity, 96%). The optical immunoassay performed well, but like other rapid tests, is not sensitive enough to replace standard culture for detection of group A beta-hemolytic streptococci.

Particle enhanced immunoaggregation of F(ab′) 2 molecules

The immunological agglutination reactions of physically adsorbed F(ab′) 2 molecules onto anionic and cationic latex particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different experimental conditions to determine the most influential factors. Surface F(ab′) 2 and BSA densities, particle concentration in the reaction medium and polyethylene glycol concentration are some of these factors. Sensitized cationic and anionic latexes differ considerably with respect to their colloidal stability and reactivity. As a general rule, the sensitized cationic latex has a relatively higher colloidal stability and hence, it provides reagents with a better optical response. Less than 0.025 μg/ml of C-reactive protein has been detected using this particle enhanced optical immunoassay.

Characterisation and optimisation of an immunoprobe for triazines.

The characterisation and optimisation of an optical immunoassay with label free detection based on Reflectometric Interference Spectroscopy (RIfS) is presented. The immunoprobe is operated in a sequential scheme, where Fab-fragments react with analyte molecules in a first step. In a second step the optical transducer is used to quantify the amount of unoccupied Fab- fragments in the reaction mixture binding to the hapten-modified transducer surface. For optimisation of the test, the Fab-fragment concentration was varied between 2x10(-8) mol/l and 2.5x 10(-9) mol/l. Down to a concentration of 5x10(-9) mol/l a reduction in the limit of detection has been observed. At the lowest concentration investigated no further improvement has been found due to a reduced binding of the analyte and a strong decrease of antibody binding at the transducer surface. This finding could be explained by the thermodynamics of the antigen-antibody reaction and the performance of the optical transducer used. The limit of detection obtained is discussed with respect to thermodynamics, transducer characteristics and immunoprobe test format.

STRATEGIES TO IMPROVE THE COLLOIDAL STABILITY AND THE REACTIVITY OF IMMUNOLATEX BEADS

ABSTRACT The aim of the present work is to study the influence of the sequential or competitive adsorption of anti-HSA (Human Serum Albumin) IgG and RSA (Rabbit Serum Albumin) onto a negatively charged polystyrene latex on the colloidal stability of the immunoiatex (IgG-RSA/latex). Anionic (1-2) latex was prepared by surfactant free emulsion polymerization. Adsorption of IgG and RSA on the latex 1-2 was performed at low ionic strength and different pHs. Sequential and competitive adsorption of a-HSA IgG and RSA were performed Colloidal stability of immunolatex was improved by RSA adsorption, especially in the competitive adsorption. In this last case, the immunological agglutination reactions of physically adsorbed IgG molecules onto anionic particles have been investigated by means of optical absorbance measurements. These measurements have been conducted under different experimental conditions to determine the most influential factors. Surface IgG and BSA densities, particle concentration in the reaction medium, and polyethylene glycol concentration are some of these factors. An amount of HSA lesser than 60 ng/ml has been possible to detect using this particle enhanced optical immunoassay.

Evaluation of two rapid antigen assays, BioStar Strep A OIA and Pacific Biotech CARDS O.S., and culture for detection of group A streptococci in throat swabs

Two rapid methods, BioStar Strep A OIA (OIA; BioStar, Inc., Boulder, Colo.), an optical immunoassay, and CARDS O.S. (O.S.; Pacific Biotech, Inc., San Diego, Calif.), a color immunochromographic assay, and two culture methods, one with 5% sheep blood agar (SBA) and one with Todd-Hewitt broth (TH; Remel, Lenexa, Kans.), were evaluated for use in the detection of Streptococcus pyogenes from pharnygeal swabs. Seven hundred forty-six double swabs (Culturette II) were processed, with OIA and SBA culture performed on one swab and O.S. and SBA culture performed on the other swab. The pledget from the Culturette II was incubated overnight in TH and was subcultured onto SBA for an additional 48 h in ambient air. All beta-hemolytic streptococci from culture were tested by a direct fluorescent-antibody test (Difco Laboratories, Detroit, Mich.). Specimens with discordant fluorescent-antibody test and rapid test results were also tested by using the Streptex latex agglutination reagent (Murex Diagnostics Limited, Dartford, England). The results obtained by all testing methods were compared with a combined test result ("gold standard"), which was defined as any positive culture detected by the SBA or TH culture methods and confirmed by Streptex latex agglutination or, in the case of negative results by both culture methods, a concomitant positive result by OIA and O.S. antigen testing. Sensitivity and specificity results for each of the methods were as follows, respectively: OIA, 81.0 and 97.5%; O.S., 74.4 and 99.0%; SBA culture, 92.3 and 98.3%; and TH culture, 86.4 and 100%. Both OIA and O.S. are suitable screening methods for detecting S. pyogenes directly from throat swabs but are of insufficient sensitivity to eliminate the need for backup cultures for specimens with negative OIA and O.S. results.