Airline travel may spread infections between passengers far more often than is reported, according to articles in the Lancet medical journal.

Travellers exposed to disease from a fellow passenger disperse widely very quickly and may be taken sick days or weeks later, often with symptoms that do not have to be reported to national public health monitors.

Conventional wisdom used to suggest that the risk was highest for people sitting within two rows of the original person carrying a bug, and even then only on flights lasting more than eight hours. But during the Sars crisis, passengers on a three-hour flight appear to have been infected up to seven rows away.

Reviewing the existing research, Mark Gendreau, of the Lahey Clinic medical centre in Burlington, Massachussets, said that airlines often kept incomplete lists of passengers, making it impossible to locate those who might have been infected on a flight.

Food poisoning was also a threat. Salmonella from airline meals alone might have infected 4,000 passengers.