Nucleic acid detection and quantitative analysis of influenza virus using exhaled breath condensate

Background: Influenza is a common respiratory infectious disease that can be transmitted by respiratory droplets from person to person. There were few researches on influenza virus in exhaled breath. This study aimed to investigate the detection of influenza virus in exhaled breath condensate (EBC) and conduct quantitative analysis to evaluate the existence and content of influenza virus in breath. Methods: We recruited 30 patients with respiratory tract infection in the 2019 influenza season. The clinical data and samples of nasal swabs were collected and rapid influenza diagnostic (antigen) tests (RIDTs) and EBC influenza virus nucleic acid detection were performed. Each sample was assessed thrice for qualitative and quantitative analysis. The patients were followed up after one month, and the EBC was assessed again. Results: The 30 cases were assessed for the presence of influenza virus nucleic acid in each EBC sample three times. The results showed that seven cases were positive for influenza A/ three times, seven cases were positive for influenza A twice, seven cases were positive for influenza A once, two cases were positive for influenza B once, and seven cases were negative for all three times. Furthermore, quantitative analysis showed that the influenza viral load in the EBC ranged from 103 to 107 copy/ml. Conclusion: The influenza virus can be detected using EBC and the concentration can be calculated. Thus, EBC can be used for molecular diagnosis of influenza.