A passenger who took a Greyhound bus from Merritt, B.C., to Calgary is being treated for tuberculosis in the Alberta city, prompting a call for others to be tested for the infectious disease.

The Calgary Health Region said the man showed up at a local hospital on Jan. 30, where he is still being treated in isolation.

Health officials in Alberta and B.C. are working with the bus company to contact all passengers who took bus 1015 on Jan. 11.

The bus, which can carry 55 passengers but was not full at the time, began its journey in Vancouver, but the infected individual boarded in Merritt at about 7:50 p.m., said the B.C. Centre for Disease Control and the Interior Health Authority Monday.

They are asking that only passengers who were on the bus from Merritt onward, including stops in Kamloops, Salmon Arm and Revelstoke, take a tuberculosis skin test.

Health officials said they're issuing a public alert because passenger records were incomplete, so they hope people from the bus will contact them. Greyhound Canada said it doesn't ask passengers for phone numbers or addresses.

Tuberculosis is spread through droplets in the air, as when an infected person coughs or sneezes, for example. The bacteria most commonly attacks the lungs and can be fatal for those who have weak immune systems, such as children or the elderly.

"The risk is very, very low to the general public," said Calgary Health Region spokeswoman Leanne Dohy.

"It's only … direct contacts, people that were on this bus and sitting close enough that they would have come in contact with any respiratory secretions from this individual that would be at any risk, and it would be a very low risk even to them."