OTTAWA, Oct. 2(Xinhuanet) -- Four more people were infected by the mysterious respiratory virus that has killed four in Toronto since outbreak, making the number of the patients up to 77, local reports said Sunday.

    Despite the encouraging recoveries so far of some patients, there has been a slight increase in the number of the sickened, Dr. David McKeown, Toronto's Medical Officer of Health, told Canadian TV (CTV) in Toronto.

    The rise of patients is not alarming so far, and many of the patients are actually improving, Mckeown said.

    "It is too early to say we're out of the woods," he said.

    A mystery respiratory virus has killed four senior residents inToronto, Canada's biggest city, since the outbreak began on Sept. 25.

    Health officials have on Saturday ruled out the deadly SARS, influenza, and avian flu as possible causes of the outbreak.

    Three hospitals that admit the patients are being isolated. Medical staff of these hospitals are all taking precautions by wearing gloves, gowns, masks and goggles. Enditem