Transmission of pandemic (H1N1) 2009 influenza on international flightsAustralia 2009

Background: The emergence of pandemic (H1N1) 2009 influenza (pH1N1) in Mexico and the United States with rapid spread to Europe and the Pacific is testament to the ease of transmission of infectious disease by international flights. Understanding the dynamics of in-flight spread is important for prioritising public health response to pandemic incursions. Therefore a study to investigate the spread of pH1N1 from confirmed cases on flights to Australia was undertaken. The spread of other influenza-like illness (ILI) was also documented.

Methods: A retrospective cohort study was conducted with questionnaires sent to all passengers on two separate flights with confirmed cases of pH1N1 entering Australia in May 2009. Questions included information on ILI symptoms; co-morbidities; onset, prophylaxis and isolation dates; and potential exposure to ILI. Triangulation of results was achieved through examining national pH1N1 notification databases.

Results: Results including survey responses from 319 (43%) of 738 passengers revealed that 13 (2%) had an ILI in-flight and 32 (5%) developed an ILI in the first week post-flight arrival. Passengers were 7.5 times more likely to contract pH1N1 if they sat in the same row or within two rows of cases who were symptomatic pre-flight. A closer exposed zone (two seats in-front, behind and either side) had the attack rate increase from 3.8% to 8.3%. Dates of isolation and anti-viral prophylaxis were available from 48 (31%) of 156 passengers contacted by health authorities. The majority of these (65%) were contacted three days or more post flight arrival.

Conclusions: Preventing community incursion of influenza following international flights would be more efficient, without compromising the effectiveness of public health interventions, if contact tracing of exposed passengers was targeted to a two-by-two square.

Key words: airline, pandemic (H1N1) 2009, influenza, contact tracing

Word count: 273

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Author (s): 

A. Ruth Foxwell12, L. Roberts12, K. Lokuge1 and P. Kelly1 1Communicable Disease and Surveillance Branch, Office of Health Protection, Department of Health and Ageing Australian Government 2National Centre for Epidemiology and Population Health, Austral

Presenter (s): 
Dr. Ruth Foxwell
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