Transmission of influenza on international flights, may 2009

Understanding the dynamics of influenza transmission on international fl ights is necessary for prioritizing public health response to pandemic incursions. A retrospective cohort study to ascertain in-fl ight transmission of pandemic (H1N1) 2009 and influenza-like illness (ILI) was undertaken for 2 long-haul fl ights entering Australia during May 2009. Combined results, including survey responses from 319 (43%) of 738 passengers, showed that 13 (2%) had an ILI in fl ight and an ILI developed in 32 (5%) passengers during the first week post arrival. Passengers were at 3.6% increased risk of contracting pandemic (H1N1) 2009 if they sat in the same row as or within 2 rows of persons who were symptomatic prefl ight. A closer exposed zone (2 seats in front, 2 seats behind, and 2 seats either side) increased the risk for postfl ight disease to 7.7%. Efficiency of contact tracing without compromising the effectiveness of the public health intervention might be improved by limiting the exposed zone.