Screening for H7N9 influenza A by matrix gene-based real-time reverse-transcription PCR

Rapid detection of novel influenza A strains, including H7N9, is pivotal to ensuring appropriate public health-based responses and real-time reverse-transcription polymerase chain reaction (RT-PCR) methods are used typically for this purpose. However, the utility of such methods can be undermined by ongoing sequence variations, particularly when targeting the variable influenza A haemagglutinin (HA) and neuraminidase (NA) genes. This may often be a source of frustration for clinical laboratories that are implementing methods in preparation for potential pandemics as primers and probe targets may need to be checked regularly and updated. In this study, screening methods were developed for H7N9 influenza A strains based on the highly-conserved influenza A matrix gene. Three assays were developed and evaluated in parallel, and included two methods which simply involved inclusion of a single H7N9 probe sequence into an established influenza A and B multiplex RT-PCR (FluAB-PCR). The detection limits of the methods were compared using ten-fold dilutions of H7N9 RNA, and the specificity of the methods were tested using 32 influenza A RT-PCR-positive samples and a panel of 18 influenza A isolates, including representives of seasonal H3N2, seasonal H1N1, pandemic H1N1, H5N1, H5N3, H9N2 and H7N7. The detection limits of the three methods were the same, and no cross-reactions were observed with sH3N2, sH1N1, pH1N1 or H5N1. However, cross-reactions were observed with H5N3, H9N2 and H7N7. Overall, the results show that the methods are useful for front-line screening for H7N9.