Rapid diagnosis of influenza: state of the art

Abstract

Much effort has been expended developing testing modalities for influenza viruses that are capable of providing rapid results to clinicians. Antigen-detection techniques, historically the only methods able to deliver results quickly, are still widely used despite concerns about sensitivity. Recently, nucleic acid amplification tests (NAATs), which can achieve rapid turnaround times and high sensitivity, have become available. In addition, NAATs can detect other respiratory pathogens. Although there are many theoretical advantages to rapid influenza testing, the clinical impact of testing in various patient populations must be considered against the cost and the analytical performance of the tests.

Keywords: Antigen; Direct immunofluorescence assays; Influenza; Nucleic acid amplification tests; Polymerase chain reaction; Rapid diagnosis; Respiratory virus.

Fig. 1

Lateral flow immunochromatography for the detection of influenza A and B. (Bottom left) The patient specimen is applied to a defined area that contains antiviral antibodies labeled with a detection molecule. Next, labeled antibodies with or without bound antigen are drawn along the test strip through capillary action. Antiviral monoclonal antibody and anti–immunoglobulin G (IgG) are immobilized at the distal end of the test strip in well-demarcated areas corresponding to influenza A or influenza B. Viral antigens mediate the retention of labeled antiviral antibodies at the test strip, and anti-IgG binds residual labeled antibodies present. (Top right) Visible or fluorescent lines appear at both the test and control locations when viral antigens are present (positive test), or the control location only when antigens are absent (negative test).

Fig. 2

Workflow of commercially available influenza virus nucleic acid amplification test. Proprietary detection methods are used by xTag, eSensor, SeePlex, and Resplex assays. Black boxes indicate steps performed on a single instrument, white spaces indicate requirement to move samples to new instrument, and white lines indicate discrete processes occurring on a single instrument. Processes are not drawn to scale. PCR, polymerase chain reaction.