Public health officials say that an infectious outbreak of unknown origin at a Toronto nursing home has been contained and seems to be winding down. They acknowledged they may never know the cause of the illness, which has killed 16 residents and sent dozens of others to area hospitals.

Ontario’s health minister called the situation at 250-bed Seven Oaks Home for the Aged a “tragedy” but was quick to calm fears that the illness might be spreading. A deadly SARS outbreak gripped the Toronto area in 2003.

Health officials say the disease, which claimed six lives on Wednesday alone, is not SARS, avian flu, flu type A or B, or Legionnaire’s Disease. More than 120 residents, employees and visitors have fallen ill from it since Sept. 25. Many exhibited coughing and flu-like systems, according to published reports. The World Health Organization said, despite the unknown origin of the outbreak, there is no reason for major concern.

While more severe cases were transported to seven area hospitals, residents with milder symptoms have remained at Seven Oaks for recovery. New admissions and visitors have been restricted during the outbreak.