The molecular epidemiology of respiratory viruses associated with asthma attacks: A single-center observational study in Japan

Few reports have described the significance of viral respiratory infections (VRIs) in exacerbation of asthma in adult patients. The aim of this study was to elucidate the profiles of VRIs in adult patients with asthma along with their molecular epidemiology. A cross-sectional observational study was conducted at Kyorin University Hospital from August 2012 to May 2015. To identify respiratory pathogens in inpatients and outpatients suffering from asthma attacks, RT-PCR/sequencing/phylogenetic analysis methods were applied alongside conventional microbiological methods. Phylogenetic and pairwise distance analyses of 10 viruses were performed. A total of 106 asthma attack patients enrolled in this study in both inpatient (n = 49) and outpatient (n = 57) settings. The total 106 respiratory samples were obtained from nasopharyngeal swab (n = 68) or sputum (n = 38). Among these, patients with virus alone (n = 39), virus and bacterial (n = 5), and bacterial alone (n = 5) were identified. The ratio of virus-positive patients in inpatient or outpatient to the total cases were 31.1% (n = 33) and 10.4% (n = 11), respectively. The frequency of virus-positive patients was significantly higher in inpatients (75.3%, n = 33) than in outpatients (19.3%, n = 11). Major VRIs included human rhinovirus (HRV) (n = 24), human metapneumovirus (hMPV) (n = 9), influenza virus (Inf-V) (n = 8), and respiratory syncytial virus (RSV) (n = 3) infections with seasonal variations. HRV-A and HRV-C were the most commonly detected viruses, with wide genetic divergence on phylogenetic analysis. Asthmatic exacerbations in adults are highly associated with VRIs such as HRV-A or HRV-C, hMPV, RSV, and Inf-V infections with seasonal variations and genetic divergence, but similar frequencies of VRIs occurred in asthma attack patients throughout the seasons.