RAPID DETECTION OF INFLUENZA VIRUSES: PERFORMANCE CHARACTERISTICS OF DIRECTIGEN EZ FLU A + B AND BINAXNOW® INFLUENZA A & B TESTS

Introduction: Rapid diagnosis of influenza viruses facilitates the use of antiviral agents, helps prevent the spread of nosocomial infections and allows clinicians to differentiate a routine cause of infection from organisms requiring antibacterial therapy. Screening for influenza by rapid tests can decrease workload and improve workflow during epidemic seasons. The purpose of our study was to analyze the performance of two immunochromatographic (IC) assays, Directigen™ EZ Flu A + B (BD Diagnostics, Sparks, MD, “DG”) and BinaxNow® Flu A & B (Inverness Medical, Binax, Scarborough, ME, “BX”) compared to a combined standard of direct immunofluorescent antigen staining (DFA) and culture on nasopharyngeal aspirates (NPAs).

Methods: NPAs collected from children and adults during 2005-2007 were included (total N=1409). NPAs were tested by DG and BX simultaneously with subsequent testing using DFA (D³ Ultra DFA Respiratory Virus Screening and ID kit, Diagnostic Hybrids, Inc., Athens, OH) and two culture formats: (1) R-Mix Too shell vials (stained with D³ Ultra screen/ID reagents after 48 hours) and (2), standard tube cultures [cynomolgus and rhesus monkey kidney cells] held for 21 days (all products by DHI). A true positive result was defined as any positive result by DFA, shell vial, or tube culture.     

Results: Influenza prevalence and IC device performance by year and stratified by age are shown in the tables below:

Conclusion: DG and BX devices perform similarly for the detection of influenza A and B in NPAs in children and adults. These devices are not adequately sensitive to be used as the sole diagnostic test for influenza viruses however they can be useful during periods of high prevalence when they can facilitate early institution of antiviral medication and help laboratories to streamline work flow.