Quantitative analysis of four rapid antigen assays for detection of pandemic H1N1 2009 compared with seasonal H1N1 and H3N2 influenza A viruses on nasopharyngeal aspirates from patients with influenza.

Data on analytical sensitivity of rapid diagnostic assays are important for clinical management of influenza, especially during a pandemic. Four rapid antigen detection assays were compared for detection of pandemic influenza A H1N1 2009, seasonal H1N1 and H3N2 in 96 patients with influenza A infection confirmed by real-time RT-PCR. These rapid antigen tests appeared to have lower sensitivity (55.8%) for the diagnosis of pandemic influenza A H1N1 2009 as compared with seasonal H3N2 (71.0%) or H1N1 (69.4%) influenza infections, a difference that was related to a lower viral load in patients infected with the pandemic influenza A H1N1 2009 virus. The detection limit of these antigen detection tests in clinical specimens was an influenza A M gene copy number of average 1.0×10(7) copies/ml. Significant variations between tests in sensitivity for detection of pandemic influenza A H1N1 2009 (43.4-63.3%) were observed. The Directigen EZ Influenza A+B and the Espline Influenza A+B had comparable sensitivity (63%) and were the most sensitive among the four assays evaluated.