title: Incidence and epidemiology of hospitalized influenza cases in rural Thailand during the influenza A (H1N1)pdm09 pandemic, 2009-2010.
abstract: BACKGROUND
  Data on the burden of the 2009 influenza pandemic in Asia are limited. Influenza A(H1N1)pdm09 was first reported in Thailand in May 2009. We assessed incidence and epidemiology of influenza-associated hospitalizations during 2009-2010.
  
  
  METHODS
  We conducted active, population-based surveillance for hospitalized cases of acute lower respiratory infection (ALRI) in all 20 hospitals in two rural provinces. ALRI patients were sampled 1∶2 for participation in an etiology study in which nasopharyngeal swabs were collected for influenza virus testing by PCR.
  
  
  RESULTS
  Of 7,207 patients tested, 902 (12.5%) were influenza-positive, including 190 (7.8%) of 2,436 children aged <5 years; 86% were influenza A virus (46% A(H1N1)pdm09, 30% H3N2, 6.5% H1N1, 3.5% not subtyped) and 13% were influenza B virus. Cases of influenza A(H1N1)pdm09 first peaked in August 2009 when 17% of tested patients were positive. Subsequent peaks during 2009 and 2010 represented a mix of influenza A(H1N1)pdm09, H3N2, and influenza B viruses. The estimated annual incidence of hospitalized influenza cases was 136 per 100,000, highest in ages <5 years (477 per 100,000) and >75 years (407 per 100,000). The incidence of influenza A(H1N1)pdm09 was 62 per 100,000 (214 per 100,000 in children <5 years). Eleven influenza-infected patients required mechanical ventilation, and four patients died, all adults with influenza A(H1N1)pdm09 (1) or H3N2 (3).
  
  
  CONCLUSIONS
  Influenza-associated hospitalization rates in Thailand during 2009-10 were substantial and exceeded rates described in western countries. Influenza A(H1N1)pdm09 predominated, but H3N2 also caused notable morbidity. Expanded influenza vaccination coverage could have considerable public health impact, especially in young children.
authors.affiliation: International Emerging Infections Program, Thailand Ministry of Public Health (MOPH) - U.S. Centers for Disease Control and Prevention Collaboration, Nonthaburi, Thailand. hbaggett@cdc.gov
authors.forename: Henry C
authors.initials: HC
authors.lastname: Baggett
authors.forename: Malinee
authors.initials: M
authors.lastname: Chittaganpitch
authors.forename: Somsak
authors.initials: S
authors.lastname: Thamthitiwat
authors.forename: Prabda
authors.initials: P
authors.lastname: Prapasiri
authors.forename: Sathapana
authors.initials: S
authors.lastname: Naorat
authors.forename: Pongpun
authors.initials: P
authors.lastname: Sawatwong
authors.forename: Darunee
authors.initials: D
authors.lastname: Ditsungnoen
authors.forename: Sonja J
authors.initials: SJ
authors.lastname: Olsen
authors.forename: James M
authors.initials: JM
authors.lastname: Simmerman
authors.forename: Prasong
authors.initials: P
authors.lastname: Srisaengchai
authors.forename: Somrak
authors.initials: S
authors.lastname: Chantra
authors.forename: Leonard F
authors.initials: LF
authors.lastname: Peruski
authors.forename: Pathom
authors.initials: P
authors.lastname: Sawanpanyalert
authors.forename: Susan A
authors.initials: SA
authors.lastname: Maloney
authors.forename: Pasakorn
authors.initials: P
authors.lastname: Akarasewi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D003625:Data Collection; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000502:physiology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D008875:Middle Aged; D058873:Pandemics / Q000706:statistics & numerical data*; D012424:Rural Population / Q000706:statistics & numerical data*; D012621:Seasons; D013785:Thailand / Q000453:epidemiology; D055815:Young Adult