title: International flight-related transmission of pandemic influenza A(H1N1)pdm09: an historical cohort study of the first identified cases in the United Kingdom.
abstract: BACKGROUND
  Transporting over two billion passengers per year, global airline travel has the potential to spread emerging infectious diseases, both via transportation of infectious cases and through in-flight transmission. Current World Health Organization (WHO) guidance recommends contact tracing of passengers seated within two rows of a case of influenza during air travel.
  
  
  OBJECTIVE
  The objectives of this study were to describe flight-related transmission of influenza A(H1N1)pdm09 during a commercial flight carrying the first cases reported in the United Kingdom and to test the specific hypothesis that passengers seated within two rows of an infectious case are at greater risk of infection.
  
  
  METHODS
  An historical cohort study, supplemented by contact tracing, enhanced surveillance data and laboratory testing, was used to establish a case status for passengers on board the flight.
  
  
  RESULTS
  Data were available for 239 of 278 (86·0%) of passengers on the flight, of whom six were considered infectious in-flight and one immune. The attack rate (AR) was 10 of 232 (4·3%; 95% CI 1·7-6·9%). There was no evidence that the AR for those seated within two rows of an infectious case was different from those who were not (relative risk 0·9; 95% CI 0·2-3·1; P = 1·00). Laboratory testing using PCR and/or serology, available for 118 of 239 (49·4%) of the passengers, was largely consistent with clinically defined case status.
  
  
  CONCLUSIONS
  This study of A(H1N1)pdm09 does not support current WHO guidance regarding the contact tracing of passengers seated within two rows of an infectious case of influenza during air travel.
authors.affiliation: Health Protection Agency, Bristol, UK.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Young
authors.forename: Richard
authors.initials: R
authors.lastname: Pebody
authors.forename: Gillian
authors.initials: G
authors.lastname: Smith
authors.forename: Babatunde
authors.initials: B
authors.lastname: Olowokure
authors.forename: Giri
authors.initials: G
authors.lastname: Shankar
authors.forename: Katja
authors.initials: K
authors.lastname: Hoschler
authors.forename: Monica
authors.initials: M
authors.lastname: Galiano
authors.forename: Helen
authors.initials: H
authors.lastname: Green
authors.forename: Anders
authors.initials: A
authors.lastname: Wallensten
authors.forename: Angela
authors.initials: A
authors.lastname: Hogan
authors.forename: Isabel
authors.initials: I
authors.lastname: Oliver
mesh_terms: D064870:Air Travel; D015331:Cohort Studies; D016358:Contact Tracing; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology / Q000635:transmission* / Q000821:virology*; D008297:Male; D006113:United Kingdom / Q000453:epidemiology
keywords: Aircraft; influenza; pandemics; prevention and control; transmission; travel