This BMJ study assessed 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.

The design was a retrospective cohort investigation using a questionnaire administered to passengers and laboratory investigation of those with symptoms.

The setting was in Auckland, New Zealand, with national and international follow-up of passengers. The participants were 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.

9 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. 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.

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.