To the Editor: Modern air travel lends itself to aerosol transmission of viral infection. Infected individuals in modern aircraft represent a significant risk for other travellers during long journeys.

In September 1999, a person with an influenza-like illness joined other workers returning by aircraft to an isolated mine in north-western Australia. He was identified as unwell by a mine supervisor in the airport lounge but was allowed to board the BAe 146 aircraft (a 75-seat passenger jet aircraft). The flight lasted 3 hours 20 minutes. On landing in the evening, most workers were transported to their quarters in a 10-minute bus trip, but some, including the affected worker, travelled independently. They then went to their individual rooms.

The next day, the affected worker reported sick immediately on going to his work site and did not work for 4 days. The other workers undertook 12-hour shifts operating machinery or in offices, relatively isolated from other people. However, they may have mixed socially.

Over the next 3–4 days, 15 other workers presented with an acute influenza-like illness, with fever, cough, nasal congestion, anorexia and prostration. No serological tests were undertaken because of the remoteness of the mine.

All other workers on the flight were contacted by telephone 6 days after the flight. Five more were identified who had significant upper respiratory tract symptoms and were taking simple analgesics, but had continued to work. The airline reported that no staff from the aircraft had reported sick over the next week or so.

The seating positions of the affected workers on the aircraft, which was full, are shown in the Box. The index patient sat in seat 11G. Most of the other affected workers appeared to sit in a “plume” around him. The only affected workers who sat further away were the supervisor who assessed the index patient in the airport lounge (seat 3A) and a person who conducted a raffle during the flight and walked the length of the aircraft collecting money and ticket stubs (seat 1F). In aircraft such as the BAe 146, air is circulated and filtered, entering the passenger compartment through continuous vents just beneath the overhead lockers, circulating downwards and exiting from continuous vents under the seats. Air therefore tends to flow in two contrarotating circles, from ceiling to floor on either side of the aircraft. Infection could well have been transmitted by aerosol droplets to passengers behind the index patient, as he coughed and sneezed throughout the flight. The immunisation status of the passengers was not recorded; most were aged 20–45 years.

This outbreak was relatively confined, as the passengers were in an isolated community, and those affected were managed in their rooms. However, the implications for the spread of airborne infection in passenger aircraft and into the wider community are obvious.

It must be stressed to the travelling public that people with this type of illness should not fly. Airport authorities at passenger check-ins should be encouraged to identify and formally assess potentially infected individuals, and should have the authority to take precautions against spread.

Aircraft seat allocations of index patient and affected passengers

I = index patient.

F = passenger developed influenza-like illness.

M = passenger developed mild upper respiratory tract illness.