While two people remain in a Calgary hospital after contracting legionnaires' disease, officials are still trying to find out what caused a local outbreak of the bacterial infection.

A total of eight people have been diagnosed as being exposed to the legionella pneumophila bacteria over the past month, and were hospitalized after experiencing serious respiratory illnesses.

"At this point in time ... we've gone through and looked at any of the potential sources that the cases have identified where they may be exposed and the testing for those possible sources has been negative so we're not identifying a risk to the public at the present time," said Dr. Brent Friesen, the area's medical officer of health.

Authorities say the disease is not spread person to person but is connected with water sources like cooling towers or air-conditioning units.

Friesen says given that legionella is normally associated with summer weather and high humidities, it's unusual for an outbreak, such as this one, to occur at this time of year.