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Transmission of pandemic A/H1N1 2009 influenza on passenger aircraft: retrospective cohort study

BMJ 2010; 340 doi: (Published 21 May 2010) Cite this as: BMJ 2010;340:c2424
  1. Michael G Baker, associate professor1,
  2. Craig N Thornley, medical officer of health2,
  3. Clair Mills, senior lecturer3,
  4. Sally Roberts, microbiologist4,
  5. Shanika Perera, medical officer of health2,
  6. Julia Peters, medical officer of health2,
  7. Anne Kelso, director5,
  8. Ian Barr, deputy director5,
  9. Nick Wilson, associate professor1
  1. 1Department of Public Health, University of Otago, Box 7343 Wellington South 6242, New Zealand
  2. 2Auckland Regional Public Health Service, Auckland District Health Board, Auckland 1150, New Zealand
  3. 3Faculty of Medical and Health Sciences, University of Auckland, Auckland
  4. 4Department of Microbiology, Auckland District Health Board, PO Box 110031, Auckland, New Zealand
  5. 5WHO Collaborating Centre for Reference and Research on Influenza, North Melbourne, Victoria 3051, Australia
  1. Correspondence to: M Baker michael.baker{at}
  • Accepted 1 March 2010


Objectives To assess the risk of transmission of pandemic A/H1N1 2009 influenza (pandemic A/H1N1) from an infected high school group to other passengers on an airline flight and the effectiveness of screening and follow-up of exposed passengers.

Design Retrospective cohort investigation using a questionnaire administered to passengers and laboratory investigation of those with symptoms.

Setting Auckland, New Zealand, with national and international follow-up of passengers.

Participants Passengers seated in the rear section of a Boeing 747-400 long haul flight that arrived on 25 April 2009, including a group of 24 students and teachers and 97 (out of 102) other passengers in the same section of the plane who agreed to be interviewed.

Main outcome measures Incidence of in-flight infection with pandemic A/H1N1; sensitivity and specificity of influenza symptoms for confirmed infection; and completeness and timeliness of contact tracing.

Results Nine members of the school group were laboratory confirmed cases of pandemic A/H1N1 infection and had symptoms during the flight. Two other passengers developed confirmed pandemic A/H1N1 infection, 12 and 48 hours after the flight. They reported no other potential sources of infection. Their seating was within two rows of infected passengers, implying a risk of infection of about 3.5% for the 57 passengers in those rows. All but one of the confirmed pandemic A/H1N1 infected travellers reported cough, but more complex definitions of influenza cases had relatively low sensitivity. Rigorous follow-up by public health workers located 93% of passengers, but only 52% were contacted within 72 hours of arrival.

Conclusions A low but measurable risk of transmission of pandemic A/H1N1 exists during modern commercial air travel. This risk is concentrated close to infected passengers with symptoms. Follow-up and screening of exposed passengers is slow and difficult once they have left the airport.


  • We thank Radhika Nagappan (LabPlus, Auckland District Health Board) and staff of the WHO Collaborating Centre for Reference and Research on Influenza (Melbourne) for laboratory work, the health workers involved in the public health response and data collection, and the passengers and the affected high school for their prompt reporting and cooperation with public health measures. The investigation of and response to this incident included staff from many agencies, notably public health units, district health boards, immigration, customs, Auckland International Airport Limited, and the Ministry of Health.

  • Contributors: MGB and CNT jointly initiated the investigation, developed the study design, managed the investigation, and drafted the paper. CM and SP managed data collection on airline passengers seated in the rear of the plane and interviewed these passengers. SR managed the laboratory testing of passengers. JP jointly initiated and managed the investigation. AK and IB jointly managed the laboratory typing of the influenza viruses and serological testing. NW jointly developed the study design. All authors read and approved the final version of the manuscript. MGB is the guarantor.

  • Funding: This investigation was largely funded by the internal resources of the investigators’ employing organisations as part of the public health response to the A/H1N1 pandemic. MGB was partly supported by a grant from the Centers for Disease Control and Prevention (USA) for research on pandemic influenza (1 U01 CI000445-01). The WHO Collaborating Centre for Reference and Research on Influenza is supported by the Australian Government Department of Health and Ageing. The funding sources had no involvement with the decision to write this paper and submit it for publication.

  • Competing interests: All authors have completed the Unified Competing Interest form at (available on request from the corresponding author) and declare: (1) MGB was partly supported by a grant from the Centers for Disease Control and Prevention (USA) for research on pandemic influenza (1 U01 CI000445-01); all other authors declare no financial support for the submitted work from anyone other than their employer; (2) No financial relationships with commercial entities that might have an interest in the submitted work; (3) No spouses, partners, or children with relationships with commercial entities that might have an interest in the submitted work; (4) No non-financial interests that may be relevant to the submitted work.

  • Ethical approval: Northern Regional Ethics Committee, Auckland gave ethics approval.

  • Data sharing: No additional data available.

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