Health officials worldwide are taking no chances with a fast moving deadly mystery virus. Severe Acute Respiratory Syndrome?or SARS?has infected at least 5,500 people including 65 in the United States, with more cases developing by the day. At least 50 deaths have been attributed to the virus so far.

Hayley Sterling reports authorities are shutting down hospitals, schools and apartment buildings from Hong Kong to Ontario in an attempt to contain the spread of the illness.

Immunologists and healthcare professionals throughout the world are growing more alarmed as they learn new characteristics of a mystery virus that spreads easily. The Centers for Disease Control president Dr. Julie Gerberding?

?The global epidemic continues to expand. Today, the WHO is reporting 1,491 cases and 54 deaths, plus the 62 cases that we are reporting here in the United States. We continue to regard the new coronavirus as the early hypothesis for the etiology of this condition. The evidence is mounting from a number of international labs that this indeed is the case; but we are also exploring other potential viruses, as are collaborators.?

Health officials in Ontario report they know of at least 100 suspected cases and have isolated three groups where spread of the virus can be traced back to?health care workers, hospital patients?and their visitors.

The first Canadian to die of SARS had just returned from a trip to Hong Kong where she contracted the illness?

?We believe, based on what the investigations have shown us so far, that the major mode of transmission still is through droplet spread when an infected person coughs or sneezes and droplets are spread to a nearby contact. But we are concerned about the possibility of airborne transmission across broader areas and also the possibility that objects that become contaminated in the environment could serve as modes of spread.?

The virus has hit mainland China the hardest. Even the doctor who first identified the virus died Saturday. The World Health Organization is particularly concerned about Hong Kong, which reports dozens of new cases daily.

Health authorities are taking no chances. This mystery illness prompts people of all ages to wear surgical masks. Public areas, elevators, lobbies and subway stations are getting disinfected. The government has imposed ten-day quarantines on anyone who has had close contact with a victim.

Epidemiologists say SARS resembles other viruses such as the common cold?but it can be contagious for up to ten days after symptoms first appear. The CDC says no current antiviral drugs or other treatments tested against SARS have been effective.