BinaxNOW Influenza Research Articles

The use of saliva specimens for detection of influenza A and B viruses by rapid influenza diagnostic tests

Background and objectivesDiagnostic tests for influenza infection commonly use nasopharyngeal swabs (NPS) even though these are invasive to obtain. As an alternative specimen, we evaluated the diagnostic usefulness of saliva samples with rapid influenza diagnostic tests (RIDTs). Study designBoth NPS and saliva samples were collected from 385 influenza suspected patients and analyzed using Sofia Influenza A+B Fluorescence Immunoassay (Quidel Corporation, San Diego, CA, USA), ichroma TRIAS Influenza A+B (Boditech, Chuncheon, Korea), SD Bioline Influenza Ag (Standard Diagnostic, Yonggin, Korea), BinaxNOW Influenza A/B antigen kit (Alere Inc., Waltham, MA, USA), and real-time reverse transcriptase PCR (RT-PCR). ResultsOf the 385 patients, 31.2% (120/385) were positive for influenza A, and 7.5% (29/385) were positive for influenza B virus with saliva or NPS by RT-PCR. The diagnostic sensitivity was slightly higher in NPS than in saliva samples for both influenza A and B by all of the four RIDTs. The diagnostic sensitivities of Sofia and ichroma TRIAS were significantly superior to those of the other conventional influenza RIDTs with both types of sample. The sensitivities of Sofia and ichroma TRIAS with saliva specimens were comparable to the sensitivities of the other two conventional RIDTs with NPS specimens. The simultaneous use of saliva and NPS samples exhibited improved sensitivity from 10.0% to 13.3% for influenza A and from 10.3% to 17.2% for influenza B compared to using NPS alone. ConclusionsThis study demonstrates that saliva is a useful specimen for influenza detection, and that the combination of saliva and NPS could improve the sensitivities of influenza RIDTs.

Diagnostic performance of influenza viruses and RSV rapid antigen detection tests in children in tertiary care

BackgroundRapid antigen detection tests (RADTs) are increasingly used to detect influenza viruses and respiratory syncytial virus (RSV). However, their sensitivity and specificity are a matter of debate, challenging their clinical usefulness. ObjectivesComparing diagnostic performances of BinaxNow Influenza AB® (BNI) and BinaxNow RSV® (BNR), to those of real-time reverse transcriptase PCR (RT-PCR), virus isolation and direct immunofluorescence (D-IF) in paediatric patients. Study designBetween November 2005 and September 2013, 521 nasal washings from symptomatic children (age <5 years) attending our tertiary care centre were tested, with a combination of the respective assays using RT-PCR as gold standard. ResultsSensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of BNI were 69% (confidence interval [CI] [51–83]), 96% [94–97], 55% [39–70] and 98% [96–99] respectively. Of eleven false-negative samples, RT-PCR Ct-values were higher than all RT-PCR positive test results (27 vs 22, p=0.012). Of twenty false-positive samples, none were culture positive and two tested positive in D-IF.Sensitivity, specificity, PPV and NPV for BNR were 79% [73–85], 98% [96–99], 97% [93–99] and 88% [84–91]. Of the 42 false-negative samples the median Ct-value was higher than that of all RT-PCR positive samples (31 vs 23, p<0.0001). Five false-positive samples were detected. Three of these tested positive for RSV in virus isolation and D-IF. ConclusionsRADTs have a high specificity with BNR being superior to BNI. However, their relative low sensitivity limits their usefulness for clinical decision making in a tertiary care paediatric hospital.

GENEDIA Multi Influenza Ag Rapid Test for detection and H1, H3, and H5 subtyping of influenza viruses

BackgroundRapid identification and subtype determination of influenza virus is important in managing infected patients. Rapid influenza diagnostic tests (RIDTs) are widely used in this manner, but most can only detect influenza A and B viruses without subtyping. A new RIDT, GENEDIA Multi Influenza Ag Rapid Test (GENEDIA), was developed for detection of influenza A and B viruses and also subtyping of influenza A to H1, H3, H5 which has not been possible with other RIDTs. ObjectivesAssess the performance of GENEDIA. Study designNasopharyngeal swabs were collected from 274 clinically suspected patients (influenza A/H1N1/2009 (n=50), influenza A/H3 (n=50), influenza B (n=73) and influenza-negative (n=101)) and analyzed with the real-time RT-PCR, GENEDIA, SD Bioline Influenza Ag, and Alere BinaxNow Influenza A&B Card. Also, 46 fecal specimens (H5N2 (n=3), H5N3 (n=3)) of spot-billed duck were analyzed with RT-PCR and GENEDIA. ResultsCompared to real-time RT-PCR, the sensitivities of GENEDIA, SD Bioline Influenza Ag, and Alere BinaxNow Influenza A&B Card were 73.0%, 57.0%, 58.0% for influenza A, respectively, and 68.5%, 65.8%, 57.5% for influenza B, respectively. Specifically, the sensitivity of GENEDIA was 70.0% for influenza A/H1N1/2009 and 76.0% for influenza A/H3. From the avian influenza samples, GENEDIA detected all six H5 subtype without any cross-reactions. ConclusionThe GENEDIA Multi Influenza Ag Rapid Test was sensitive in detecting influenza viruses compared with other commercial RIDTs and also useful for rapid subtype determination of influenza A.

Evaluation of Xpert® Ebola Assay performance with whole blood, plasma, and buccal swab sample types

Rapid identification and subtype determination of influenza virus is important in managing infected patients. Rapid influenza diagnostic tests (RIDTs) are widely used in this manner, but most can only detect influenza A and B viruses without subtyping. A new RIDT, GENEDIA Multi Influenza Ag Rapid Test (GENEDIA), was developed for detection of influenza A and B viruses and also subtyping of influenza A to H1, H3, H5 which has not been possible with other RIDTs.Assess the performance of GENEDIA.Nasopharyngeal swabs were collected from 274 clinically suspected patients (influenza A/H1N1/2009 (n = 50), influenza A/H3 (n = 50), influenza B (n = 73) and influenza-negative (n = 101)) and analyzed with the real-time RT-PCR, GENEDIA, SD Bioline Influenza Ag, and Alere BinaxNow Influenza A&B Card. Also, 46 fecal specimens (H5N2 (n = 3), H5N3 (n = 3)) of spot-billed duck were analyzed with RT-PCR and GENEDIA.Compared to real-time RT-PCR, the sensitivities of GENEDIA, SD Bioline Influenza Ag, and Alere BinaxNow Influenza A&B Card were 73.0%, 57.0%, 58.0% for influenza A, respectively, and 68.5%, 65.8%, 57.5% for influenza B, respectively. Specifically, the sensitivity of GENEDIA was 70.0% for influenza A/H1N1/2009 and 76.0% for influenza A/H3. From the avian influenza samples, GENEDIA detected all six H5 subtype without any cross-reactions.The GENEDIA Multi Influenza Ag Rapid Test was sensitive in detecting influenza viruses compared with other commercial RIDTs and also useful for rapid subtype determination of influenza A.

Evaluation of 3 rapid influenza diagnostic tests during the 2012–2013 epidemic: influences of subtype and viral load

This article evaluates the performance of 3 rapid influenza diagnostic tests (RIDTs), in correlation with the influenza subtypes and the viral load. A total of 236 samples were prospectively analyzed with BinaxNOW Influenza A/B, Directigen EZ Flu A and B, and bioNexia Influenza A+B. The results were compared to cell cultures and real-time polymerase chain reaction. Positive samples were further subtyped. Thirty-seven samples were positive for influenza A, and 57, for influenza B. For A(H1N1), the sensitivities were 71.42% for BinaxNOW, 78.57% for Directigen, and 67.85% for bioNexia. Eight samples were positive for A(H3N2), and only the bioNexia test had 1 false-negative result. Lowest sensitivities were observed for influenza B/Yamagata, (56.86% for BinaxNOW and Directigen and 39.21% for bioNexia). The 3 evaluated RIDTs were more efficient at detecting influenza A(H3N2) than for A(H1N1) and B/Yamagata. Highest viral loads in the samples were associated with better rate of detection.

Comparison of the BD Veritor System for Flu A+B with the Alere BinaxNOW Influenza A&amp;B Card for Detection of Influenza A and B Viruses in Respiratory Specimens from Pediatric Patients

The performance characteristics of two commercially available rapid tests for influenza, the BD Veritor System for Flu A+B (BD) and the Alere BinaxNOW influenza A&B card (BN), were evaluated using 200 frozen clinical specimens collected from January 2011 to June 2012 from pediatric patients. Real-time reverse transcriptase PCR (RT-PCR) was used as the gold standard to evaluate the results obtained by the two different assays. Of the 200 specimens tested, real-time RT-PCR assay detected influenza A or B virus in 116 samples, while BD detected 104 samples and BN detected 84 samples as positive. The overall sensitivity and specificity for detection of both influenza A and B virus in comparison to those of real-time RT-PCR were 89.6% (95% confidence interval [CI], 82.2 to 94.3) and 98.8% (95% CI, 92.6 to 99.9) for BD Veritor and 72.4% (95% CI, 63.2 to 80.0) and 100% (95% CI, 94.5 to 100.0) for BinaxNOW. Workflow analysis indicated that overall processing times for a batch size of 10 specimens were virtually identical between both systems. Overall, these results indicate that the BD Veritor assay was more sensitive than the BinaxNOW assay in detection of influenza A and B viruses in respiratory specimens from pediatric patients.

Clinical and Virologic Factors Associated with Reduced Sensitivity of Rapid Influenza Diagnostic Tests in Hospitalized Elderly Patients and Young Children

ABSTRACTRapid influenza diagnostic tests (RIDTs) are commonly used by clinicians to guide patient management. Data on sensitivities among hospitalized patients are limited. Here, we evaluated the clinical and virologic factors affecting the sensitivities of 2 commercially available RIDTs (BinaxNOW Influenza A&amp;B and QuickVue Influenza A+B) on nasopharyngeal aspirate (NPA) specimens collected from elderly patients and young children hospitalized for influenza. Influenza cases and age-matched negative controls were prospectively enrolled during the 2011-2012 influenza season in Hong Kong. NPA specimens were collected at presentation before antiviral treatment. Real-time reverse transcription-PCR (RT-PCR) results were used as references for the sensitivity analyses. One hundred patients (57 influenza cases and 43 controls) were studied. Both RIDTs had 100% specificities. The sensitivities of the BinaxNOW Influenza A&amp;B and QuickVue Influenza A+B tests were 70% and 82%, respectively. For both tests, the sensitivities were lower in cases with presentation times beyond 2 days of illness onset than for those within this time (50 to 71% versus 85 to 91%, respectively). There were trends toward lower sensitivities for influenza B than for influenza A (66 to 81% versus 76 to 84%, respectively), among young children than among the elderly patients (63 to 78% versus 80 to 88%, respectively), and among cases with pneumonia than those without pneumonia (75% versus 82 to 94%, respectively). The sensitivities of the RIDTs decreased with reduced NPA viral RNA levels (5.6 to 15.0% reduction per 1-log decrease), which declined progressively after illness onset (Spearman's rho, −0.47 [P&lt; 0.05] and −0.66 [P&lt; 0.001] for influenza A and B, respectively). Collectively, late presentation, a low NPA viral load, and probably lower respiratory manifestation are factors associated with reduced sensitivities of RIDTs for diagnosing influenza in hospitalized patients. A negative RIDT result should be interpreted with caution.

Impact of the Availability of an Influenza Virus Rapid Antigen Test on Diagnostic Decision Making in a Pediatric Emergency Department

Fever is one of the most commonly seen symptoms in the pediatric emergency department. The objective of this study was to observe how the rapid testing for influenza virus impacts on the management of children with fever. We performed a review of our pediatric emergency department records during the 2008/2009 annual influenza season. The BinaxNow Influenza A+B test was performed on patients with the following criteria: age 1.0 to 16.0 years, fever greater than 38.5 °C, fever of less than 96 hours' duration after the onset of clinical illness, clinical signs compatible with acute influenza, and nontoxic appearance. Additional laboratory tests were performed at the treating physician's discretion. The influenza rapid antigen test was performed in 192 children. One hundred nine (57%) were influenza positive, with the largest fraction (101 patients) positive for influenza A. The age distribution did not differ between children with negative and positive test results (mean, 5.3 vs. 5.1 years, not statistically significant). A larger number of diagnostic tests were performed in the group of influenza-negative patients. Twice as many complete blood counts, C-reactive protein determinations, lumbar punctures, and urinalyses were ordered in the latter group. Rapid diagnosis of influenza in the pediatric emergency department affects the management of febrile children as the confirmation of influenza virus infection decreases additional diagnostic tests ordered.

Evaluation of Sofia fluorescent immunoassay analyzer for influenza A/B virus

BackgroundThe influenza virus causes seasonal epidemics which are associated with high morbidity and mortality. Rapid diagnostics tests (RDT) are frequently used to make a quick influenza diagnosis to confirm the clinical suspicion, despite their low sensitivity. ObjectivesAssess the performance of the Sofia Influenza A+B Fluorescence Immunoassay (Quidel, San Diego, CA). Study designNasopharyngeal swabs, taken from 241 patients (influenza A (n=73)/B (n=72), negative samples (n=96)) were analyzed using the Sofia Influenza A+B Fluorescence Immunoassay, BinaxNOW Influenza A/B antigen kit (Alere Inc., USA), Directigen EZ Flu A and B (Becton Dickinson, USA), real-time RT-PCR and an influenza virus culture. ResultsThere was a significant difference between the performance of rapid antigen tests and the Sofia FIA, when compared to the RT-PCR, in the detection of influenza strain A and B. Indeed, the Sofia FIA displayed sensitivities of 82.2% and 77.8% for strains A and B respectively, whereas sensitivities of BinaxNOW Influenza A/B antigen kit, and Directigen Flu A and B were 54.8%, and 68.5% for influenza A, and 62.5%, and 52.8% for influenza B respectively. The average RT-PCR threshold cycle (Ct) (±SD) for the Sofia Influenza A+B Fluorescence Immunoassay-positive specimens was higher than those of the BinaxNOW Influenza A/B antigen and the Directigen EZ Flu A and B kit positive specimens. ConclusionCompared to other RDTs, the Sofia Influenza A+B Fluorescence Immunoassay is a sensitive, and rapid method for the detection and discrimination between influenza A and B.

Comparison of Xpert Flu rapid nucleic acid testing with rapid antigen testing for the diagnosis of influenza A and B

Influenza infections are associated with thousands of hospital admissions and deaths each year. Rapid detection of influenza is important for prompt initiation of antiviral therapy and appropriate patient triage. In this study the Cepheid Xpert Flu assay was compared with two rapid antigen tests, BinaxNOW Influenza A & B and BD Directigen EZ Flu A+B, as well as direct fluorescent antibody testing for the rapid detection of influenza A and B. Using real-time, hydrolysis probe-based, reverse transcriptase PCR as the reference method, influenza A sensitivity was 97.3% for Xpert Flu, 95.9% for direct fluorescent antibody testing, 62.2% for BinaxNOW, and 71.6% for BD Directigen. Influenza B sensitivity was 100% for Xpert Flu and direct fluorescent antibody testing, 54.5% for BinaxNOW, and 48.5% for BD Directigen. Specificity for influenza A was 100% for Xpert Flu, BinaxNOW, and BD Directigen, and 99.2% for direct fluorescent antibody testing. All methods demonstrated 100% specificity for influenza B. These findings support the use of the Xpert Flu assay in settings requiring urgent diagnosis of influenza A and B.

Diagnostic performance of the BinaxNow Influenza A&B rapid antigen test in ED patients

ObjectiveThe objective of this study is to evaluate the diagnostic performance of the BinaxNow Influenza A&B rapid antigen test (RAT) in emergency department (ED) patients. MethodsWe prospectively enrolled a systematic sample of ED patients older than 6 months with acute respiratory symptoms or nonlocalizing fever during 3 consecutive influenza seasons (2008-2011). Nasal and throat swabs collected by research personnel were tested for influenza by real-time reverse transcription–polymerase chain reaction (RT-PCR). Clinicians independently ordered RATs during clinical care; these specimens were collected by clinical staff and tested for influenza using the BinaxNow RAT. Patients with both a research RT-PCR and clinical RAT were included in the study. Rapid antigen test diagnostic performance was evaluated using RT-PCR as a criterion standard, with preplanned, stratified analysis for subject age, duration of symptoms, influenza subtype, and polymerase chain reaction cycle threshold, which provides a semiquantitative estimate of viral load. ResultsOf 561 subjects enrolled, 131 (23.4%) had a positive RT-PCR, and 37 (6.6%) had a positive RAT. Overall, RAT performance included sensitivity of 24.4% (95% confidence interval [CI], 17.5%-32.9%), specificity of 98.8% (95% CI, 97.1%-99.6%), positive predictive value of 86.5% (95% CI, 70.4%-94.9%), negative predictive value of 81.1% (95% CI, 77.4%-84.3%). Rapid antigen test sensitivities were low for all categories of subject age, symptom duration, influenza subtype, and cycle threshold. ConclusionThe BinaxNow RAT demonstrated high specificity and poor sensitivity in ED patients selected by treating clinicians for influenza testing. A negative RAT is a poor predictor for the absence of influenza in the ED and should not be used as a criterion to withhold antiviral medications.

Variations in Positive Predictive Values for Rapid Influenza Tests for 2009 Pandemic Influenza A (pH1N1)—Arizona, April-October 2009

Rapid influenza diagnostic tests (RIDTs) are used for influenza screening, clinical decision making, and influenza surveillance. In August 2009, a hospital reported increased false-positive RIDT results to the Arizona Department of Health Services. Because of reported RIDT low sensitivities (40%-62%) for 2009 pandemic influenza A (pH1N1), the hospital's report raised further concerns about the specificity and clinical utility of RIDTs. To determine the positive predictive value (PPV) of RIDTs compared with real-time reverse transcription-polymerase chain reaction assay (rRT-PCR) using Centers for Disease Control and Prevention (CDC) protocols and primers as a standard. A standardized survey collected information including RIDT brand/lot number, training of personnel performing test, type of laboratory, swab and specimen type, time from collection to testing, sample storage, and viral transport medium. Arizona. Seven Arizona laboratories submitted positive RIDT clinical samples to Arizona State Public Health Laboratory (ASPHL) for confirmatory rRT-PCR testing. The PPV was calculated on the basis of rRT-PCR-positive results for April through October. Results from 600 specimens using 1 of 4 RIDTs were available. Median pH1N1 PPV was 80% (range: 62%-91%) when calculated by RIDT brand. A significant difference in PPV was identified between the 2 largest facilities, which used the same RIDT brand, BinaxNOW Influenza A&B, (Laboratories A, 33% and B, 92%, [P < .01]). The facilities reported similar testing practices except lot numbers used and timing of testing. Laboratory A used lot 003684 and performed testing within 1 hour of collection; Laboratory B used multiple lots, excluding lot 003684, and performed testing within 24 hours. Laboratory A switched RIDT brands and noted a significant PPV increase from 33% to 91% (P < .01). Wide PPV variability combined with documented low sensitivity among RIDTs for pH1N1 diagnosis increases concerns about their specificity and clinical and epidemiologic utility for influenza.

PROSPECTIVE EVALUATION OF CORIS INFLU-A&B RESPI-STRIP AND OF BINAXNOW INFLUENZA A&B ASSAY AGAINST VIRAL CULTURE AND REAL-TIME PCR ASSAY FOR DETECTION OF 2009 PANDEMIC INFLUENZA A/H1N1V IN BELGIAN PATIENTS

Purpose – Evaluation of the performance of two rapid (15’) antigen detection tests (RAT), BinaxNOW Influenza A&B and Coris Influ-A&B Respi-Strip for the detection of A(H1N1)v2009.Study design – Between July 2009 and November 2009, 4105 respiratory specimens from patients with influenza-like illness attending seven public hospitals in Brussels were prospectively examined by two immunochromatographic RAT, followed by viral culture and/or specific real-time RT-PCR.Results – Samples consisted predominantly of nasopharyngeal aspirates (NPA-41%), nasopharyngeal (NPS- 37%) and throat swabs (TS-14%). The sensitivity and specificity of Coris RAT and BinaxNOW RAT were 36.6% and 99.7%, and 47% and 98.7% respectively compared to culture; and 33.7% and 99.6%; and 46.5% and 98.8% compared to RT-PCR. Significant differences in sensitivity could be observed when splitting up the samples by sample type and patient’s age. NPA gave by far the highest sensitivities: 51.1- 62% for Coris compared to culture and 62.6-78.4% for BinaxNOW. Sensitivities in paediatric NPS varied less between different hospitals (34-41.9%) being still much higher than in adult NPS (11.4-20%). TS resulted in unsatisfactory results: 13% sensitivity in children and 10.5% in adults.Conclusions – Both RAT showed excellent specificities, but insufficient sensitivities. Consequently, negative results should be confirmed. NPA are clearly superior to NPS or TS, and they stay the sample of choice for viral diagnosis.

Evaluation of the ESPLINE® Influenza A &amp; B-N assay for the detection of influenza A and B in nasopharyngeal aspirates

Several direct antigen tests for the detection of influenza often lack sensitivity compared to immunofluorescence (IF) on the specimens and viral culture (VC). We evaluated the performance of a rapid test, the ESPLINE® Influenza A & B-N assay. A total of 302 respiratory specimens were collected at the University Hospital of Antwerp. A first group of 60 samples taken during the H1N1 outbreak (2009-2010) and a second group of 242 samples stored during the seasonal influenza epidemics (2000-2009) were analyzed with the ESPLINE® test. A subset of samples were also evaluated with the BinaxNOW Influenza and the Clearview Exact Influenza. The results were compared to IF on the specimens, VC with IF, and the combination of both, which was considered as the gold standard. The ESPLINE® test's overall sensitivity and specificity were 91% and 97%, during the H1N1 season 80% and 93%, and for the detection of seasonal influenza 93% and 97%, respectively. In comparison to the BinaxNOW Influenza and the Clearview Exact Influenza, all tests demonstrated a similar specificity of 92.0-100% but a significantly different sensitivity of 44.4-86.0%, with the ESPLINE® test being significantly more sensitive. Due to its very good performance and simplicity, the ESPLINE® test facilitates urgent testing. The test seems less sensitive to detect H1N1 compared to seasonal influenza, although the difference is borderline not significant (p = 0.067).

Comparison of a laboratory-developed RT-PCR and the CDC RT-PCR protocol with rapid immunodiagnostic testing during the 2009 H1N1 influenza A pandemic

We evaluated the performance of a laboratory-developed multiplex real-time reverse transcription-PCR assay (LDT rRT-PCR), the Centers for Disease Control and Prevention (CDC) 2009 H1N1 rRT-PCR protocol using the LightCycler 480 II, the multiplex xTAG Respiratory Virus Panel (xTAG RVP), and rapid immunodiagnostic testing (RIDT) using the BinaxNOW Influenza A & B to detect 2009 H1N1 with 426 nasopharyngeal swab specimens during the 2009 H1N1 pandemic. The specificity of the methods tested was ≥98%, and the individual test sensitivities were RIDT at 42.3% [95% confidence interval (CI), 31.4–54.0], LDT rRT-PCR at 98.9% (95% CI, 92.9–99.9), CDC 2009 H1N1 rRT-PCR at 78.2% (95% CI, 67.8–86.0), and xTAG RVP at 93.1% (95% CI, 85.0–97.2). A negative RIDT result should not be used to make decisions with respect to treatment or infection prevention. rRT-PCR is the preferred first-line diagnostic test for detecting 2009 H1N1 influenza A.

Comparative Analysis of the Multiple Test Methods for the Detection of Pandemic Influenza A/H1N1 2009 Virus

Accurate and rapid diagnosis of Pandemic Influenza A/H1N1 2009 virus (H1N1 2009) infection is important for the prevention and control of influenza epidemics and the timely initiation of antiviral treatment. This study was conducted to evaluate the performance of several diagnostic tools for the detection of H1N1 2009. Flocked nasopharyngeal swabs were collected from 254 outpatients of suspected H1N1 2009 during October 2009. This study analyzed the performances of RealTime ready Inf A/H1N1 Detection Set (Roche), Influenza A (H1N1) Real-Time Detection Kit (Bionote), Seeplex Influenza A/B OneStep Typing set (Seeplex reverse transcriptase PCR [RT-PCR]), BinaxNow Influenza A & B test kit (Binax rapid antigen test [RAT]) and SD BIOLINE Influenza Ag kit (SD RAT). Roche and Bionote real-time RT-PCR showed identical results for the H1N1 2009 hemagglutinin gene. Compared with real-time RT-PCR, the sensitivities and specificities were 83.7% and 100% for Seeplex RT-PCR, 64.5% and 94.7% for Binax RAT, and 69.5% and 100% for SD RAT. The sensitivities of Seeplex RT-PCR, Binax RAT and SD RAT in patients aged over 21 years were 73.7%, 47.4% and 57.9%, respectively. The sensitivities of Seeplex RT-PCR, Binax RAT and SD RAT on the day of initial symptoms were mostly lower (68.8%, 56.3% and 31.3%, respectively). In conclusion, multiplex RT-PCR and RAT for the detection of H1N1 2009 were significantly less sensitive than real-time RT-PCR. Also, a negative RAT may require more sensitive confirmatory assays, because it cannot be ruled out from influenza infection.

Utility of the rapid antigen detection BinaxNOW Influenza A&B test for detection of novel influenza A (H1N1) virus

Nasopharyngeal aspirates, collected during outbreaks, of the novel influenza A (H1N1) virus in Barcelona, were used to compare the accuracy of a rapid antigen-based test (Binax) with the real-time RT-PCR assay developed by the CDC. The sensitivity, specificity and positive predictive value of the rapid test are higher in patients less than 18 years old and during the acute stage of the epidemic than in adult patients.

Comparison of BinaxNOW Influenza A&B assay and real-time reverse transcription polymerase chain reaction for diagnosis of influenza A pandemic (H1N1) 2009 virus infection in adult patients

The BinaxNOW Influenza A&B assay was evaluated for the diagnosis of influenza A pandemic (H1N1) 2009 virus infection in 354 adult patients. The sensitivity, specificity, and positive and negative predictive values were 32%, 100%, 100%, and 67%, respectively. The analytic sensitivity of the assay was log 10 5.0 tissue culture infective dose (TCID) 50/mL.

Rapid Antigen Test for Pandemic (H1N1) 2009 Virus

To the Editor: Drexler et al. recently compared the sensitivity of the BinaxNOW Influenza A & B Rapid Test (BinaxNOW; Inverness Medical, Cologne, Germany) with that of a real-time reverse transcription–PCR (RT-PCR) assay specific for influenza A pandemic (H1N1) 2009 virus (1). Of 1,838 clinical specimens tested, 221 were confirmed as positive for pandemic (H1N1) 2009 by RT-PCR. When 144 of these 221 specimens were evaluated by using the BinaxNOW, results were positive for only 16 (11%). At onset of the pandemic, we evaluated the first 135 nasopharyngeal aspirates submitted to the Regional Laboratory of Public Health Haarlem, the Netherlands. We compared the performance of the BinaxNOW for diagnosing influenza A (H1N1) virus by using molecular detection of influenza virus as the reference standard. Samples were analyzed with a general influenza A assay targeting the matrix gene (the RespiFinder assay) (PathoFinder B.V., Maastricht, the Netherlands [2]) and a pandemic (H1N1) 2009–specific RT-PCR assay targeting the neuraminidase gene (3). We tested 135 patient samples (76 from male patients); mean age of patients was 32 years (range 0–81 years). Samples from 38 (28%) patients had positive results in both RT-PCRs, and samples from 97 (72%) patients had negative results in the matrix gene RT-PCR and neuraminidase RT-PCR assays. Sensitivity and specificity were estimated to be 47% (18/38, 95% confidence interval [CI] 32%–62%) and 95% (92/97, 95% CI 88%–98%), respectively, for the BinaxNOW antigen test. Patients’ ages did not significantly differ between rapid test–positive and –negative results. Our results largely agree with those of Vasoo et al. (4) and the Centers for Disease Control and Prevention (5). Those studies determined that the sensitivity of the BinaxNOW compared with nucleic acid amplification tests is ≈40%. The lower sensitivity observed by Drexler et al. (1) might be because of differences in study type (retrospective evaluation compared with a prospective cohort in our study), sample size, technical factors (with regard to specimen collection, specimen transport, and specimen storage), differences in the test kit, and differences between individual patients (multiple categories of age and stages of illness, differences in virus shedding). Many clinicians are not aware of the performance of specific test devices and rely on test results to make clinical decisions. Because negative results cannot rule out influenza, this test is of little use in a clinical setting without appreciation of the limitations of the test. However, because the BinaxNOW has reasonable specificity, it might prove useful in clinical or epidemiologic situations in which test sensitivity is not critical, e.g., in facility outbreaks in which multiple specimens are collected to rapidly identify the causative organism.

Rapid Antigen Tests for Diagnosis of Pandemic (Swine) Influenza A/H1N1

We found that the sensitivities of 3 rapid influenza antigen tests for pandemic influenza A/H1N1 virus were low to moderate: BD Directigen EZ Flu A+B test (Becton Dickinson), 46.7%; BinaxNOW Influenza A&B (Inverness Medical), 38.3%; and QuickVue Influenza A+B Test (Quidel), 53.3%. A patient with influenza-like illness who has a negative rapid antigen test result should undergo further testing using reverse-transcription polymerase chain reaction.