Clinical features of three patients with co-infection of influenza A and B viruses and the molecular characteristics of the viruses

Objective To analyze the clinical features of three patients with co-infection of influenza A and influenza B viruses, and to analyze the gene mutations of the viruses. Methods Fluorescence quantitative PCR was used to detect and classify nucleic acids in respiratory specimens. The whole genomes of influenza virus were amplified and were sequenced by next-generation sequencing. The molecular characteristics of hemaglutin (HA) and neuramindase (NA) of the viruses were analyzed by bioinformatics methods. The clinical data of the patients were collected and analyzed simultaneously. Results All three patients had at least one underlying disease. Lesions in both lungs were found in two patients and two patients died. For the co-infected influenza viruses, influenza A virus strains belonged subtype H1N1, genetic group 6B.1. Three variations of amino acid in antigenic locus were detected while no significant change in drug-resistance locus was observed . The influenza B virus strains belonged to Yamagata lineages, no significant change was observed in drug-resistance locus. Conclusions The patients with co-infection of influenza A and B virus accompanied by abnormal lung/liver function had poor prognosis. The HA and NA genes were relatively conservative and no new variants were found. Key words: Influenza A virus; Influenza B virus; Co-infection; Clinical features; Molecular characteristics