title: Swine outbreak of pandemic influenza A virus on a Canadian research farm supports human-to-swine transmission.
abstract: BACKGROUND
  Swine outbreaks of pandemic influenza A (pH1N1) suggest human introduction of the virus into herds. This study investigates a pH1N1 outbreak occurring on a swine research farm with 37 humans and 1300 swine in Alberta, Canada, from 12 June through 4 July 2009.
  
  
  METHODS
  The staff was surveyed about symptoms, vaccinations, and livestock exposures. Clinical findings were recorded, and viral testing and molecular characterization of isolates from humans and swine were performed. Human serological testing and performance of the human influenza-like illness (ILI) case definition were also studied.
  
  
  RESULTS
  Humans were infected before swine. Seven of 37 humans developed ILI, and 2 (including the index case) were positive for pH1N1 by reverse-transcriptase polymerase chain reaction (RT-PCR). Swine were positive for pH1N1 by RT-PCR 6 days after contact with the human index case and developed symptoms within 24 h of their positive viral test results. Molecular characterization of the entire viral genomes from both species showed minor nucleotide heterogeneity, with 1 amino acid change each in the hemagglutinin and nucleoprotein genes. Sixty-seven percent of humans with positive serological test results and 94% of swine with positive swab specimens had few or no symptoms. Compared with serological testing, the human ILI case definition had a specificity of 100% and sensitivity of 33.3%. The only factor associated with seropositivity was working in the swine nursery.
  
  
  CONCLUSIONS
  Epidemiologic data support human-to-swine transmission, and molecular characterization confirms that virtually identical viruses infected humans and swine in this outbreak. Both species had mild illness and recovered without sequelae.
authors.affiliation: University of Alberta, Edmonton, Alberta, Canada. sarah.forgie@albertahealthservices.ca
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Forgie
authors.forename: Julia
authors.initials: J
authors.lastname: Keenliside
authors.forename: Craig
authors.initials: C
authors.lastname: Wilkinson
authors.forename: Richard
authors.initials: R
authors.lastname: Webby
authors.forename: Patricia
authors.initials: P
authors.lastname: Lu
authors.forename: Ole
authors.initials: O
authors.lastname: Sorensen
authors.forename: Kevin
authors.initials: K
authors.lastname: Fonseca
authors.forename: Subrata
authors.initials: S
authors.lastname: Barman
authors.forename: Adam
authors.initials: A
authors.lastname: Rubrum
authors.forename: Evelyn
authors.initials: E
authors.lastname: Stigger
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Marrie
authors.forename: Frank
authors.initials: F
authors.lastname: Marshall
authors.forename: Donald W
authors.initials: DW
authors.lastname: Spady
authors.forename: Jia
authors.initials: J
authors.lastname: Hu
authors.forename: Mark
authors.initials: M
authors.lastname: Loeb
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Russell
authors.forename: Lorne A
authors.initials: LA
authors.lastname: Babiuk
mesh_terms: D000328:Adult; D000416:Alberta / Q000453:epidemiology; D000818:Animals; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission / Q000821:virology*; D008297:Male; D017720:Molecular Epidemiology; D009976:Orthomyxoviridae Infections / Q000662:veterinary* / Q000821:virology; D012367:RNA, Viral / Q000235:genetics; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D013552:Swine; D013553:Swine Diseases / Q000453:epidemiology* / Q000821:virology*
chemical_list: D012367:RNA, Viral