A Study on viral etiologies of lower respiratory infections and molecular characterization of influenza virus H1N1 2009 circulating in central Vietnam

Respiratory infections are the most important cause of worldwide burden of disease in children and a major cause of mortality. In this study, viral etiologies of lower respiratory infections from children hospitalized in central Vietnam were detected by polymerase amplification assays. Total viral etiology was 46% and relative frequencies were 45% for influenza A virus, 42% for respiratory syncytial virus, 12% for adenoviruses, 8% for influenza B virus, and 5% both for parainfluenza type 1 and 3 virus. Influenza A (H1N1) 2009 virus was mainly responsible for infections in children from 3 months to 5 years of age. Detection of influenza A (H1N1) 2009 virus was performed both by isolation on MDCK cell culture and embryonated eggs and by amplification assays. In a group of 53 suspected patients A (H1N1) 2009 virus was detected in 32(60.4%) with a combination of both methods, and virus was isolated by cell culture in 24 patients. Characterization of HA and NA genes from representative isolates of influenza A (H1N1) 2009 virus was performed. Similarity of HA gene among Hue representative isolates are from 99.48% to 99.77% and similarity of NA sequences are from 99.57% to 99.86%. The sequences of HA and NA of Hue representative isolates were compared with 18 reference isolates from different countries showing similarity from 99.07% to 99.77% for HA and from 98.65% to 99.36% for NA sequences. Phylogenetic trees based on HA and NA sequences were constructed.