title: Impact of 2009 pandemic influenza among Vietnamese children based on a population-based prospective surveillance from 2007 to 2011.
abstract: BACKGROUND
  Influenza virus is one of the major viral pathogens causing pediatric acute respiratory infection (ARI). The spread of pandemic influenza A (A(H1N1)pdm09) in 2009 around the globe had a huge impact on global health.
  
  
  OBJECTIVE
  To investigate the impact of A(H1N1)pdm09 on pediatric ARI in Vietnam.
  
  
  METHODS
  An ongoing population-based prospective surveillance in central Vietnam was used. All children aged <15 years residing in Nha Trang city, enrolled to the ARI surveillance in Khanh Hoa General Hospital, from February 2007 through March 2011 were studied. Clinical data and nasopharyngeal swab samples were collected. Influenza A was detected and genotyped by multiplex polymerase chain reaction assays and sequencing.
  
  
  RESULTS
  Among enrolled 2736 hospitalized ARI cases, 354 (13%) were positive for influenza A. Genotyping results revealed that seasonal H3N2 and H1N1 (sea-H1N1) viruses were cocirculating before A(H1N1)pdm09 appeared in July 2009. The A(H1N1)pdm09 replaced the sea-H1N1 after the pandemic. The majority of influenza A cases (90%) were aged <5 years with incidence rate of 537 (387-775) per 100 000 population. Annual incidence rates of hospitalized influenza cases for pre-, initial and post-pandemic periods among children aged <5 year were 474, 452, and 387 per 100 000, respectively. Children with A(H1N1)pdm09 were elder, visited the hospital earlier, less frequently had severe signs, and were less frequently associated with viral coinfection compared with seasonal influenza cases.
  
  
  CONCLUSIONS
  The A(H1N1)pdm09 did not increase the influenza annual hospitalization incidence or disease severity compared with seasonal influenza among pediatric ARI cases in central Vietnam.
authors.affiliation: Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan; National Institutes of Hygiene and Epidemiology, Hanoi, Vietnam; Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Minh Nhat
authors.initials: MN
authors.lastname: Le
authors.forename: Lay Myint
authors.initials: LM
authors.lastname: Yoshida
authors.forename: Motoi
authors.initials: M
authors.lastname: Suzuki
authors.forename: Hien Anh
authors.initials: HA
authors.lastname: Nguyen
authors.forename: Huu Tho
authors.initials: HT
authors.lastname: Le
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Moriuchi
authors.forename: Duc Anh
authors.initials: DA
authors.lastname: Dang
authors.forename: Koya
authors.initials: K
authors.lastname: Ariyoshi
mesh_terms: D000293:Adolescent; D044466:Asian People; D002648:Child; D002675:Child, Preschool; D062665:Epidemiological Monitoring; D005260:Female; D006760:Hospitalization; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000473:pathology / Q000821:virology; D008297:Male; D058873:Pandemics; D011446:Prospective Studies; D012720:Severity of Illness Index; D014744:Vietnam / Q000453:epidemiology
keywords: Influenza; Vietnam; pandemic; pediatric