Diagnostic performance of rapid influenza antigen assays in patients infected with the new influenza A (H1N1) virus.

BACKGROUND The new swine influenza (H1N1) requires fast and accurate diagnosis. Currently, there are few reports about the diagnostic performance of influenza antigen tests with regard to the H1N1 virus infection. We evaluated the reactivity of eight commercially available rapid antigen tests in samples from confirmed infected patients. METHODS From 23 patients tested positive by polymerase chain reaction (PCR), parallel testing with the antigen tests QuickVue Influenza A+B (Quidel Corporation), Binax NOW Flu A and B (Binax), Clearview Exact Influenza A and B (Inverness medical), TRUFLU (Meridian Bioscience), Directigen EZ Flu A+B (Becton Dickinson), Influenza A and B (Diagnostik Nord), Xpect Flu A and B (remel) and Influenza Antigen Quick (Generic Assays) was performed. RESULTS Only few antigen tests showed positive reactivity in six of the 23 samples. The virus load of the reactive samples as indicated by the PCR cycle threshold was high. Negative results of rapid influenza tests do not rule out infection with the new influenza A (H1N1) virus. Their analytical sensitivity with reference to the virus load is low and not reproducible. CONCLUSIONS As reliable laboratory results during a pandemic are essential, the diagnostic use of rapid influenza tests seems to be questionable.