Report of two cases of influenza virus A/H1N1v and B co-infection during the 2010/2011 epidemics in the Italian Veneto Region

The influenza epidemic in the 2010/2011 season has been characterized in Italy, as in the rest of the world, by a significant co-circulation of influenza A (mostly H1N1v) and influenza B viruses [1]. 1403 nasopharyngeal swabs from hospitalized patients displaying influenza-like illness underwent virological evaluation at the Microbiology and Virology Unit of the Padova Hospital, the Italian Veneto Region reference laboratory for the diagnosis of influenza and other respiratory diseases. In particular, the viral RNA was extracted from the specimens (NucliSENS？ easyMAG？, Biomerieux, Lyon, France) and a standardized controlled real time Reverse Transcription Polymerase Chain Reaction (RT-PCR) was performed [2]. This method allows the detection of influenza A and B viruses and the analysis of influenza A specific sub-types. In more details, roughly 70 ng of RNA extracted from each sample were assayed with 5 different primer and probe sets specific for influenza A, influenza B, A/H1N1v, A/H3N2 and the housekeeping gene RNasi-P. Overall 327 (23, 3%) samples were positive for influenza virus. Among the positive samples 62 were positive for influenza B virus (25%) and 265 for influenza A virus (75%) with a sharp prevalence of A/H1N1v (183 samples, 69%) over the A/H3N2 (6 samples, 2.2%). It has to be mentioned that 28.8% of influenza A virus positive samples could not be sub-typed, likely due to a low efficiency of the H1N1v specific real time adopted. A similar observation was reported during last influenza season by different European laboratories, adopting this same controlled diagnostic system [1]. The age distribution shows a prevalence of positive patients in the > 60 year old category, as expected during and epidemic season of influenza. Interestingly these data, that are in line with the results reported by different laboratories in the northern hemisphere [1], show a significant co-circulation of influenza A and influenza B viruses, with in general higher prevalence