Scientists investigating the rapid spread of the Sars virus earlier this year say they have evidence that air travel played a role.
More than 800 people died in the global Sars outbreak
But experts found that the Severe Acute Respiratory Syndrome was passed on only in cases where carriers exhibited the symptoms of the virus.
The study, in The New England Journal of Medicine, said passengers who sat closest to carriers were most at risk.
Sars killed over 800 people, infecting up to 8,000, in the worldwide outbreak.
In the course of their research, the international team of scientists interviewed passengers and crew who had flown with patients infected with Sars.
In one flight alone, 22 out of 119 people on board might have been infected by just one individual, they said
It appeared that people seated up to three rows in front of infected passengers were most at risk of contracting the disease, the report's authors said.
They said no passengers were known to have contracted Sars on flights where a person was carrying the Sars virus but was not yet showing the symptoms.
In another article in the same publication, researchers in Toronto, Canada, said the findings may explain why in most cases transmission of the virus occurred in hospital.
The BBC's health correspondent, Ania Lichtarowicz, says the research highlights how vitally important it is to identify Sars cases early and to take precautions before infected individuals can transmit the virus further.
In the latest suspected outbreak of the disease, authorities in Singapore quarantined 70 people who came into contact with a scientist who tested positive for Sars on Wednesday.