Diagnostic tests for influenza infection

The 2009 H1N1 pandemic focused attention on the speed and accuracy of influenza diagnostic methods. This review provides an update on current tests and new developments.

Widely used rapid antigen tests and immunofluorescence tests were generally less sensitive for 2009 H1N1 influenza than for seasonal influenza. In addition, marked variability was reported for the same tests in different settings and patient groups. The advantages of molecular testing gained wide recognition, namely high sensitivity, speed compared with culture, ability to assess viral load and to identify subtype. Although adoption of influenza molecular testing can be expected to accelerate, immunoassays and rapid cultures performed on site retain advantages for many facilities. Falsely negative results were seen with all methods, especially for samples collected very early or late.

Influenza diagnostic test performance can be adversely affected by viral genetic and antigenic changes and should be re-assessed annually. Variability in sensitivity and specificity of the same test in different settings highlights the need for each laboratory to ensure optimal procedures and work with clinicians to improve sample quality. Manufacturers have been motivated to improve immunoassays and develop simpler and faster multiplex molecular tests, hopefully in advance of the next pandemic.