title: Evidence for subclinical avian influenza virus infections among rural Thai villagers.
abstract: BACKGROUND
  Regions of Thailand reported sporadic outbreaks of A/H5N1 highly pathogenic avian influenza (HPAI) among poultry between 2004 and 2008. Kamphaeng Phet Province, in north-central Thailand had over 50 HPAI poultry outbreaks in 2004 alone, and 1 confirmed and 2 likely other human HPAI infections between 2004 and 2006.
  
  
  METHODS
  In 2008, we enrolled a cohort of 800 rural Thai adults living in 8 sites within Kamphaeng Phet Province in a prospective study of zoonotic influenza transmission. We studied participants' sera with serologic assays against 16 avian, 2 swine, and 8 human influenza viruses.
  
  
  RESULTS
  Among participants (mean age 49.6 years and 58% female) 65% reported lifetime poultry exposure of at least 30 consecutive minutes. Enrollees had elevated antibodies by microneutralization assay against 3 avian viruses: A/Hong Kong/1073/1999(H9N2), A/Thailand/676/2005(H5N1), and A/Thailand/384/2006(H5N1). Bivariate risk factor modeling demonstrated that male gender, lack of an indoor water source, and tobacco use were associated with elevated titers against avian H9N2 virus. Multivariate modeling suggested that increasing age, lack of an indoor water source, and chronic breathing problems were associated with infection with 1 or both HPAI H5N1 strains. Poultry exposure was not associated with positive serologic findings.
  
  
  CONCLUSIONS
  These data suggest that people in rural central Thailand may have experienced subclinical avian influenza infections as a result of yet unidentified environmental exposures. Lack of an indoor water source may play a role in transmission.
authors.affiliation: Department of Virology, US Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Benjawan P
authors.initials: BP
authors.lastname: Khuntirat
authors.forename: In-Kyu
authors.initials: IK
authors.lastname: Yoon
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Blair
authors.forename: Whitney S
authors.initials: WS
authors.lastname: Krueger
authors.forename: Malinee
authors.initials: M
authors.lastname: Chittaganpitch
authors.forename: Shannon D
authors.initials: SD
authors.lastname: Putnam
authors.forename: Krongkaew
authors.initials: K
authors.lastname: Supawat
authors.forename: Robert V
authors.initials: RV
authors.lastname: Gibbons
authors.forename: Sirima
authors.initials: S
authors.lastname: Pattamadilok
authors.forename: Pathom
authors.initials: P
authors.lastname: Sawanpanyalert
authors.forename: Gary L
authors.initials: GL
authors.lastname: Heil
authors.forename: John A
authors.initials: JA
authors.lastname: Friary
authors.forename: Ana W
authors.initials: AW
authors.lastname: Capuano
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Gray
mesh_terms: D000328:Adult; D000367:Age Factors; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D058345:Asymptomatic Infections / Q000453:epidemiology*; D015331:Cohort Studies; D004196:Disease Outbreaks / Q000662:veterinary; D005260:Female; D006801:Humans; D053124:Influenza A Virus, H5N1 Subtype / Q000276:immunology / Q000302:isolation & purification; D053127:Influenza A Virus, H9N2 Subtype / Q000276:immunology / Q000302:isolation & purification; D009980:Influenza A virus / Q000276:immunology* / Q000302:isolation & purification; D005585:Influenza in Birds / Q000453:epidemiology / Q000635:transmission / Q000821:virology; D007251:Influenza, Human / Q000453:epidemiology / Q000821:virology; D008297:Male; D008875:Middle Aged; D009976:Orthomyxoviridae Infections / Q000453:epidemiology* / Q000635:transmission / Q000821:virology; D011200:Poultry; D011201:Poultry Diseases / Q000453:epidemiology* / Q000635:transmission / Q000821:virology; D011446:Prospective Studies; D012307:Risk Factors; D012424:Rural Population; D012737:Sex Factors; D013552:Swine; D013785:Thailand / Q000453:epidemiology; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral