A blood clot caused the death of a South African woman on board a Via Rail train last week in an incident that sparked a full-scale health scare.

Dr. William Lucas, with the Ontario Coroner's Office, told The Canadian Press Monday that 43-year-old Brenda Buckley died of a pulmonary embolism.

The condition occurs when an artery in the lung becomes blocked. The blockage is generally caused by one or more blood clots that travel to the lungs from another part of the body.

Lucus could not confirm reports that the clot was the result of deep-vein thrombosis -- which can develop when people sit for long periods of time. He did say, however, it was a likely cause.

An officer with the Ontario Provincial Police told CTV.ca he could not disclose the cause of death because it falls under the Privacy Act. He said police stopped investigating the case when it was deemed the passenger died of "natural causes."

Buckley died on the train, which was travelling from Jasper, Alta., to Sudbury, Ont. on Friday. The train was stopped and quarantined about 100 kilometres west of Timmins, Ont.

An ill passenger was flown by helicopter to a Timmins hospital and five others on the train also developed respiratory and flu-like symptoms.

The coincidence had public health officials worried there might be some type of infectious disease outbreak occurring.

However, after investigating, they determined the death was unrelated to the other cases.

Catherine Kaloutsky, a spokeswoman for Via Rail, said Monday that no one has ever died from deep-vein thrombosis on one of Via Rail's trains.

She also said, unlike a plane, there are opportunities for passengers to get up and walk during a long train ride.

"They have to get up to go and eat because there's no 'at-your-seat' service, so they get up to go to the snack bar," Kaloutsky told CTV.ca.

The train also stops frequently to allow passengers time to get some "fresh air and walk around," said Kaloutsky.

Kaloutsky said she had no information as to whether Buckley did get up and walk around during the trip.

Kaloutsky said staff will review the possibility of alerting passengers to the condition in the future.

The six who became ill were Australian tourists who boarded the train in Jasper, Alta.