Evaluation of the Binax NOW, BD Directigen, and BD Directigen EZ assays for detection of respiratory syncytial virus

The Binax NOW assay (Binax, Inc., Portland, Maine) and the BD Directigen EZ assay (Becton Dickinson and Company, Sparks, Md.), two new rapid immunoassays for detection of respiratory syncytial virus (RSV), as well as the BD Directigen RSV assay (DRSV) (Becton Dickinson and Company) and direct immunofluorescence staining (DFA) were compared with culture for detection of RSV in fresh specimens from both children and adults during the 2002-2003 respiratory virus season. The majority (95%) of specimens were nasal or nasopharyngeal washes or aspirates. A total of 47 (26%) were culture positive for RSV. The overall sensitivities of DFA (n = 149), NOW (n = 118), EZ (n = 88), and DRSV (n = 180) compared with culture (n = 180) were 93, 89, 59, and 77%, respectively. The specificities of DFA, NOW, EZ, and DRSV were 97, 100, 98, and 96%, respectively. However, when results were separated into those from children and those from adults, DFA was the only rapid test adequate for detection of RSV (sensitivity of 100% compared to 0, 0, and 25% for NOW, EZ, and DRSV, respectively) in adults. For children the sensitivities of DFA, NOW, EZ, and DRSV were 93, 94, 72, and 81%. The NOW assay was the most sensitive and specific and the easiest to perform of the kit tests for detecting RSV in children. None of these three rapid kit tests was sensitive for detecting RSV in specimens from adults. DFA remains the rapid method of choice for detecting RSV in the adult population.     

Comparison of directigen RSV with viral isolation and direct immunofluorescence for the identification of respiratory syncytial virus.

An enzyme immunoassay membrane test (Directigen RSV) for the detection of respiratory syncytial virus in clinical specimens was compared prospectively with isolation in cell culture and direct immunofluorescence (IF). A total of 315 nasopharyngeal wash specimens from pediatric patients were examined. Directigen RSV was 86.1% sensitive and 91.3% specific for specimens positive by isolation in cell culture and/or IF, with 88.6% agreement. The false-positive rate was 16%; 2 of 20 specimens giving false-positive reactions by Directigen RSV were true-positives by blocking assay. Twenty-seven specimens (8.5%) whose results were initially uninterpretable by Directigen RSV due to filtration difficulties were diluted and upon retesting produced acceptable results. Sixty-three viral isolates and/or IF identifications of virus antigens representing seven virus groups other than respiratory syncytial virus were also found; cross-reactions between Directigen RSV and other viruses were not observed. Directigen RSV will be useful as an immediate procedure and in facilities lacking a comprehensive virology laboratory.     

Evaluation of a new rapid influenza A diagnostic test for detection of pandemic (H1N1) 2009 and seasonal influenza A virus

BackgroundRapid influenza A diagnostic tests (RIDTs) play an important role in the clinical setting, especially in the influenza post-pandemic era with three influenza A viruses in circulation.ObjectivesDetermine the sensitivity and specificity of a new RIDT (FluA Dot) by comparison with BD Directigen EZ FluA+B and CDC rRT-PCR.Study designTwo sets of experiments were conducted to determine the performance of the new test. (1) Serial dilutions of eight pandemic (H1N1) 2009 (pH1N1) isolates, five seasonal H3N2 isolates, five seasonal H1N1 isolates and three recombinant nucleoproteins were tested by FluA Dot assay, Directigen EZ FluA+B test and CDC real-time RT-PCR. (2) Using CDC rRT-PCR as the gold standard, the clinical sensitivity and specificity of the FluA Dot and Directigen EZ FluA+B were evaluated in nasopharyngeal swab (NPS) specimens of 807 patients presenting with influenza-like illness.ResultsThe average analytical sensitivity of FluA Dot (0.06 ng/mL for recombinant nucleoproteins and 2.16 ± 0.85 log 10 TCID₅₀ for viruses) was approximately 10-fold higher than Directigen EZ FluA+B (1–2 ng/mL for recombinant nucleoproteins and 3.54 ± 0.81 log 10 TCID₅₀ for viruses), and was approximately 10-fold lower than the CDC rRT-PCR (1.09 ± 0.69 log 10 TCID₅₀ for viruses). Among 807 NPS specimens tested, the sensitivities and specificities of FluA Dot were 91.1% (95%CI: 86.7–94.4%)/99.7% (95%CI: 98.7–99.9%), and the Directigen EZ FluA+B were 71.9% (95%CI: 65.7–77.6%)/99.8%(95%CI: 99.0–99.9%).ConclusionThe new test (FluA Dot) exhibit higher sensitivity than Directigen EZ FluA+B both in pH1N1 and seasonal influenza A detection. The promising RIDT can play important roles in influenza diagnosis and therapy.     

Evaluation of three immunoassay kits for rapid detection of influenza virus A and B

Influenza causes high morbidity and mortality in very young and elderly individuals, which can be controlled with antivirals and/or vaccines. The success of therapeutic measures is predicated on the rapid and precise diagnosis of the infection. We compared three rapid influenza immunoassay (RIIA) kits for the diagnosis of influenza virus A and B using 178 respiratory specimens submitted for routine testing. BD Directigen Flu A+B (Directigen), Directigen EZ Flu A+B (EZ), and NOW Flu A NOW Flu B (NOW; Binax) tests had comparable combined influenza virus A and B specificities, varying from 94 to 98%. In contrast, the sensitivity of EZ was significantly lower (39%) than that of NOW (76%) and marginally lower than that of Directigen (56%). The differences in sensitivity were most evident in patients who were >9 years old (Directigen, 53%; EZ, 32%; and NOW, 69%). Among specimens, bronchoalveolar lavage fluids yielded the most discrepant results, with sensitivities varying from 0 (EZ) to 100% (NOW), followed by nasopharyngeal swabs (sensitivities of 27 to 100%) and nasal washes (50 to 81%). The Directigen kit format allowed for faster completion but more cumbersome performance and more difficult interpretation compared with the other two kits. Overall, NOW provided the most accurate diagnoses and had user-friendly technical characteristics. However, the low overall sensitivity of the RIIAs indicates that these can be used as screening tools only.     

Evaluation of Three Immunoassay Kits for Rapid Detection of Influenza Virus A and B

Influenza causes high morbidity and mortality in very young and elderly individuals, which can be controlled with antivirals and/or vaccines. The success of therapeutic measures is predicated on the rapid and precise diagnosis of the infection. We compared three rapid influenza immunoassay (RIIA) kits for the diagnosis of influenza virus A and B using 178 respiratory specimens submitted for routine testing. BD Directigen Flu A+B (Directigen), Directigen EZ Flu A+B (EZ), and NOW Flu A NOW Flu B (NOW; Binax) tests had comparable combined influenza virus A and B specificities, varying from 94 to 98%. In contrast, the sensitivity of EZ was significantly lower (39%) than that of NOW (76%) and marginally lower than that of Directigen (56%). The differences in sensitivity were most evident in patients who were >9 years old (Directigen, 53%; EZ, 32%; and NOW, 69%). Among specimens, bronchoalveolar lavage fluids yielded the most discrepant results, with sensitivities varying from 0 (EZ) to 100% (NOW), followed by nasopharyngeal swabs (sensitivities of 27 to 100%) and nasal washes (50 to 81%). The Directigen kit format allowed for faster completion but more cumbersome performance and more difficult interpretation compared with the other two kits. Overall, NOW provided the most accurate diagnoses and had user-friendly technical characteristics. However, the low overall sensitivity of the RIIAs indicates that these can be used as screening tools only.     

Viral agents causing lower respiratory tract infections in hospitalized children: evaluation of the Speed-Oligo? RSV assay for the detection of respiratory syncytial virus

Respiratory syncytial virus (RSV) is the viral agent which is more frequently involved in lower respiratory tract infections (LRTIs) in infants under 1 year of age in developed countries. A new oligochromatographic assay, Speed-Oligo? RSV, was designed and optimized for the specific detection and identification of RSV subtypes A and B. The test was evaluated in 289 clinical samples from 169 hospitalized children using an immunochromatography (IC) test, virus isolation by culture, and an in-house real-time polymerase chain reaction (RT-PCR). Other viruses causing LRTIs were investigated by cell culture or PCR-based tests. Sixty-two patients were infected by RSV (36.7%). In addition, adenovirus, influenza B, parainfluenza 2, and human metapneumovirus were detected in rates ranging from 5 to 8%. A proportion of 10.1% of the patients had mixed infections. The sensitivity, specificity, and positive and negative predictive values were, respectively, 94.9, 99.4, 98.9, and 97.4% for Speed-Oligo? RSV, 92.9, 96.3, 92.9, and 96.3% for RT-PCR/RSV, and 58.4, 98.1, 93.3, and 82.6% for IC. Our rates of viral detection and co-infection were similar to those of previously reported series. Finally, we find that Speed-Oligo? RSV is a rapid and easy-to-perform technique for the detection of RSV and the identification of subtypes A and B.     

Evaluation of three rapid enzyme immunoassays and cell culture for detection of respiratory syncytial virus

Three rapid enzyme immunoassay techniques for the detection of respiratory syncytial virus antigen (Becton Dickinson Directigen RSV, Abbott RSV Testpack and Abbott RSV EIA) and cell culture were evaluated in a total of 250 nasal washings. The sensitivity and specificity were 62 % and 76 % respectively for Directigen, 64 % and 86 % for RSV Testpack, and 76 % and 81 % for RSV EIA, taking cell culture as the reference method. Agreement between cell culture and EIA techniques was 79 % (70 positive and 128 negative results). All three EIA techniques gave positive results in 69 samples (52 positive and 17 negative in the cell culture). In 121 samples all three EIA techniques gave negative results (103 negative and 18 positive in the cell culture). Using the cell culture technique 46 strains other than respiratory syncytial virus were isolated.     

Evaluation of the QuickLab RSV test, a new rapid lateral-flow immunoassay for detection of respiratory syncytial virus antigen

Rapid respiratory syncytial virus (RSV) diagnosis is vital to the prevention of nosocomial RSV infections. We evaluated a new rapid lateral-flow RSV immunoassay, the QuickLab RSV test, that requires use of only one reagent. We compared QuickLab to the Directigen RSV (DIR) assay, which requires six reagents, and direct fluorescent antibody (DFA) testing. DFA results were considered the "gold standard." For 133 nasopharyngeal aspirates tested, DFA results were 77 (57.8%) positive, 47 (35.3%) negative, and 9 (6.8%) indeterminate. The sensitivities, specificities, positive predictive values, and negative predictive values of QuickLab and DIR tests were 93.3% (70 of 75) and 80.8% (59 of 73), 95.6% (43 of 45) and 100.0% (46 of 46), 97.2% (70 of 72) and 100.0% (59 of 59), and 89.6% (43 of 48) and 76.7% (46 of 60), respectively. QuickLab was significantly (P = 0.02) more sensitive than DIR; the difference in specificities was not significant. DFA was more sensitive than DIR (P < 0.001) but not more sensitive than QuickLab (P = 0.45). The results of DIR testing were initially uninterpretable and required retesting with 15% of the specimens compared to 3% of QL results (P < 0.001). We conclude that the QuickLab RSV test has sensitivity similar to that of the DFA assay and better than that of the DIR assay. QuickLab testing is also simpler to perform and interpret than both DFA and DIR testing.     

Evaluation of five methods for respiratory syncytial virus detection.

A total of 117 nasal aspirates were cultured for respiratory syncytial virus (RSV) and tested for RSV antigen by a direct fluorescent-antibody (DFA) test (Bartels Immunodiagnostic Supplies, Inc., Bellevue, Wash.), the Directigen enzyme immunoassay (EIA; Becton Dickinson Microbiology Systems, Cockeysville, Md.), the TestPack EIA (Abbott Laboratories, North Chicago, Ill.), and RSV EIA (Abbott). Agreement of two of five methods or a positive RSV culture were required to validate a result. A total of 57 of 117 (48.7%) specimens were culture positive in HEp-2 cells, A549 cells, or both. A total of 5 of 117 (4.3%) additional specimens met the criteria of a positive specimen; i.e., 62 of 117 (53.0%) specimens were positive. Results obtained from 77 of 117 (65.8%) specimens were concordant for all five methods. The sensitivities, specificities, and positive and negative predictive values for the culture and DFA methods were 91.9, 100, 100, and 91.7% and 91.9, 96.4, 96.6, and 91.4%, respectively. The sensitivities, specificities, and positive and negative predictive values for the three EIA procedures, Directigen, TestPack, and RSV EIA, were 75.8, 80.0, 81.0, and 74.6%; 93.6, 100, 100, and 93.2%; and 71.0, 100, 100, and 75.3%, respectively. New self-contained EIA configurations and the DFA method offer attractive alternatives to the culture method. Technical simplicity, rapid turnaround time, performance, and cost must all be considered when selecting a system for RSV detection.     

Reliability of two new test kits for rapid diagnosis of respiratory syncytial virus infection.

Two new rapid enzyme immunoassays (EIAs) for detecting respiratory syncytial virus (RSV), Directigen (Becton Dickinson Microbiology Systems) and TestPack (Abbott Diagnostics) were compared with virus isolation and direct immunofluorescence by using fresh specimens. The sensitivities of both EIAs were low (72 to 73%), but when initial specimens were used, TestPack had a high sensitivity (92%) in contrast to that of Directigen (76%). Because of its high sensitivity and specificity, TestPack can be used for diagnosis of RSV in acute disease.     

Rapid diagnosis of respiratory syncytial virus infections in immunocompromised adults.

Although rapid antigen detection methods for the documentation of respiratory syncytial virus (RSV) infections are widely used with pediatric patients, these tests have not been prospectively evaluated in immunocompromised (IC) adults. For bone marrow transplant recipients and adult patients undergoing chemotherapy for leukemia who had recent onset of respiratory symptoms, respiratory samples (combined nasal wash [NW]-throat swab [TS], endotracheal tube [ET] aspirate, or bronchoalveolar lavage [BAL] samples) were collected for simultaneous culture and rapid antigen detection with the Directigen test kit (Becton Dickinson, Cockeysville, Md.). NW specimens from hospitalized pediatric patients with suspected RSV infection were also evaluated. Viral quantitation was performed on aliquots of the original specimens. A total of 539 samples from 372 adult patients were evaluated. RSV was isolated from 56 specimens (40 NW-TS, 7 ET aspirate, and 9 BAL specimens). By using culture as the "gold standard," rapid antigen detection had a sensitivity of 15% for adult NW-TS specimens, 71.4% for ET aspirate specimens, and 88.9% for BAL specimens; the specificity was > or = 97% for all specimen types. Significantly greater viral quantities were present in pediatric NW specimens than in adult NW specimens. In adults, more virus was present in BAL and ET aspirate specimens than in NW-TS specimens. Rapid detection of antigen respiratory samples obtained from the lower respiratory tracts of IC adults is sensitive and specific, but detection in upper respiratory tract samples is insensitive. The lower sensitivity of antigen detection in NW-TS specimens may be due to decreased viral load. A BAL specimen is more sensitive than an NW-TS specimen for the rapid diagnosis of RSV disease in IC adults.     

Evaluation of an enzyme membrane immunoassay (Directigen RSV) for the rapid diagnosis of respiratory syncytial virus infections

A rapid enzyme immunoassay (EIA) membrane test, the Directigen respiratory syncytial virus (Becton Dickinson), was compared with cell culture, an indirect immunofluorescence (IF) test, the Monofluokit respiratory syncytial virus (Diagnostics Pasteur), and a conventional enzyme immunoassay antigen test, the Abbott respiratory syncytial virus enzyme immunoassay in nasal aspirates specimens from children with suspected respiratory syncytial virus (RSV) bronchiolitis. The sensibility and specificity of the Directigen, respiratory syncytial virus were 91% and 98% respectively, as compared with those of culture, and of 93% and 86% as compared with the Monofluokit respiratory syncytial virus. In the comparison of the two enzyme immunoassays, Directigen respiratory syncytial virus detected more positive specimens: 68/127 than the other: 46/127. Directigen respiratory syncytial virus is a very rapid test, (15-min), sensitive and specific, which can be used as an alternative technique for detection of respiratory syncytial virus in nasal samples when viral isolation or immunofluorescence direct are not available.     

A rapid test for detection of respiratory syncytial virus in nasopharyngeal secretion

A new rapid membrane enzyme immunoassay (MEIA; Directigen RSV) for detection of respiratory syncytial virus (RSV) was evaluated using samples of nasopharyngeal secretion from infants and children with acute respiratory disease. The MEIA was compared with an immunofluorescent antibody (IF) technique using a sensitive biotin-avidin (BA) EIA as reference. Of 242 samples tested, 108 were positive by the MEIA and 123 by the BA-EIA. Of 144 samples which were also tested by the IF technique, 57 were positive by the BA-EIA and 43 by the IF technique. These results give a sensitivity of 86 % and 72 % for the MEIA and IF technique respectively. Of 57 samples found to be positive by the BA-EIA, 41 were positive by the IF technique, but 48 were positive by the MEIA. The MEIA is thus more sensitive than the IF technique but less sensitive than the BA-EIA in detecting RSV in nasopharyngeal secretions.     

Evaluation of the Directigen Group A Strep test kit

The Directigen Group A Strep test kit (Hynson, Wescott, and Dunning, Baltimore, Md.) was tested for its ability to detect group A streptococci directly from 147 throat swabs. The results were compared with results from conventional culture and Lancefield serological grouping tests. The data showed that 121 of 124 culture-negative throat specimens were also Directigen negative (98%) and that 21 of 23 culture-positive specimens were Directigen positive (91%). If specimens that provided less than 10 colonies per plate of beta-hemolytic streptococci were eliminated, all of the culture-positive specimens were Directigen positive. Positive or negative results were available within 65 to 70 min of testing. The Directigen method is relatively simple to perform and easy to interpret and provides accurate assessment of the presence or absence of group A streptococci in throat swabs, with little or no cross-reactivity with other beta-hemolytic groups.