Evaluation of 11 Commercially Available Rapid Influenza Diagnostic Tests

United States, 2011-2012

Eric Beck, PhD; Jiang Fan, MD; Kelly Hendrickson, MD; Swati Kumar, MD; Roxanne Shively, MS; William Kramp, PhD; Julie Villanueva, PhD; Daniel Jernigan, MD; Alexander Klimov, PhD; Li-Mei Chen; Ruben Donis, PhD; Tracie Williams; James Pirkle, MD, PhD; John Barr, PhD


Morbidity and Mortality Weekly Report. 2012;61(43):873-876. 

In This Article


Accurate diagnosis of influenza is critical for clinical management, infection control, and public health actions to minimize the burden of disease. Commercially available rapid influenza diagnostic tests (RIDTs) that detect the influenza virus nucleoprotein (NP) antigen are widely used in clinical practice for diagnosing influenza because they are simple to use and provide results within 15 minutes; however, there has not been a recent comprehensive analytical evaluation of available RIDTs using a standard method with a panel of representative seasonal influenza viruses. This report describes an evaluation of 11 Food and Drug Administration (FDA)–cleared RIDTs using 23 recently circulating influenza viruses under identical conditions in a laboratory setting to assess analytical performance. Most RIDTs detected viral antigens in samples with the highest influenza virus concentrations, but detection varied by virus type and subtype at lower concentrations. Clinicians should be aware of the variability of RIDTs when interpreting negative results and should collect test samples using methods that can maximize the concentration of virus antigen in the sample, such as collecting adequate specimens using appropriate methods in the first 24–72 hours after illness onset. The study design described in this report can be used to evaluate the performance of RIDTs available in the United States now and in the future.

As part of a collaboration between CDC, the Biological Advanced Research and Development Authority, and the Medical College of Wisconsin (MCW), CDC provided 16 influenza A and seven influenza B viruses to MCW to evaluate RIDTs commercially available during the 2011–12 influenza season ( Table ). Stock viruses were representative of viruses circulating in the United States since 2006 and were characterized by their 50% egg infectious dose (EID50M/mL, a measure of virus infectivity). In addition, the concentration of influenza virus NP antigen (the antigen detected by RIDTs) was measured as μg/mL using isotope dilution tandem mass spectrometry.[1] EID50/mL values were at least as high as those reported in human clinical specimens.[2–4] MCW prepared swab samples or mock nasal wash specimens from several dilutions of each virus in saline. For nine of 11 RIDTs, 50 μL of virus dilution was applied to swabs provided in the test kit or swabs described in the manufacturer's instructions for use. Two RIDTs (both manufactured by SA Scientific) require use of nasal wash specimens. Therefore, for the SA Scientific tests, 50 μL from each virus dilution first was added to saline. All samples, either prepared swabs or liquid, were added to RIDTs and incubated, with results interpreted as described in the instructions for use. Three separate tests were performed for each combination of virus and RIDT.

The numbers of RIDTs that were positive (defined as at least two positive results of the three tests performed) at each dilution for each of the 23 influenza viruses were compared ( Table ). RIDTs overall had fewer positive results with viruses that had the lowest stock NP concentrations (<2 μg/mL). Each influenza virus had variable levels of positivity with RIDTs, suggesting that several viruses of each type and subtype should be evaluated with each RIDT on a regular basis. NP levels of influenza B virus stocks generally were higher, and the first two dilutions were detected more uniformly than for influenza A viruses. No significant performance differences were noted for B/Victoria or B/Yamagata lineages of influenza B viruses.

The numbers of positive test results for each of the 11 RIDTs by influenza virus type and influenza A subgroup were compared (Figure). One RIDT (SAS FluAlert Influenza A [SA Scientific]) did not uniformly detect influenza A (H1N1)pdm09 (pH1N1) viruses or other influenza A viruses at high concentrations. Four RIDTs detected the majority of influenza B viruses in third dilution samples, whereas only one RIDT (BD Directigen EZ Flu A+B [Becton, Dickinson and Co.]) detected at least 50% of all influenza A viruses in third dilution samples.


Number of positive samples in each dilution and percentage of positive samples in each virus group, by RIDT kit — United States, 2012
Abbreviation: RIDT = rapid influenza diagnostic test.
* Four influenza A (H1N1) 2009 pandemic (pH1N1) viruses with three samples at each dilution (12 possible positive samples for each dilution).
Six pre-pandemic "seasonal" influenza A (H1N1) viruses with three samples at each dilution (18 possible positive samples for each dilution).
§ Six influenza A (H3N2) viruses with three samples at each dilution (18 possible positive samples for each dilution).
Seven influenza B viruses with 3 samples at each dilution (21 possible posiive samples for each dilution).
** CLIA-waived (i.e., exempt from all regulatory procedures typically required under Clinical Laboratory Improvement Amendments).