Comparison of two real-time RT-PCR-based systems for the detection and typing of the pandemic influenza A virus, 2009.

During the 2009 pandemic the Virology Laboratory of L. Spallanzani, Rome, Italy, adopted a real-time RT-PCR developed by the Centers for Disease Control and Prevention (CDC), Atlanta, Georgia to diagnose pandemic influenza A/H1N1 (H1N1pdm). A new multiplex real-time RT-PCR distributed by Astra Diagnostics, coupled with the extraction system developed and commercialized by Siemens Healthcare Diagnostics (referred to as the RealStar system), was tested for the ability to detect and type influenza A in clinical samples, with particular emphasis on influenza A-positive samples untyped by the CDC method. Seventy-six nasopharyngeal swabs, resulting by the CDC method H1N1pdm (n=7), H3N2 (n=3), and not subtyped (n=66), were re-analysed with the RealStar system. All H3N2 and H1N1pdm-positive samples were correctly identified; among the untyped samples, the RealStar system detected 24/66 (36.4%) H1N1pdm and 1/66 (1.5%) seasonal influenza A. In conclusion, the RealStar system confirmed the results of all the influenza A-positive samples subtyped by the CDC method, and was able to type 37.9% of samples untyped by the CDC method. However, 62.1% of samples, detected as influenza A-positive but not subtyped by the CDC method, were found to be negative by the RealStar system. Further investigation is needed to explain this latter, unexpected, finding.