Epidemic from China is encircling globe. (Morbid Mystery Tour).

An outbreak of deadly pneumonia that seems to have begun in southern China spread this month to at least two other continents, including North America. Initial tests have given clues to the identity of the pathogen involved in the infection, which health officials have dubbed severe acute respiratory syndrome (SARS).

At least 300 cases of SARS have been tallied in mainland China, where the epidemic has apparently been smoldering since last November. Elsewhere, more than 450 cases and at least 17 deaths have been attributed to the disease, according to the World Health Organization (WHO) in Geneva.

The new epidemic "reminds us that ... an emerging problem in one part of the world will soon be a problem for all of us," said Julie Gerberding, director of the Centers for Disease Control and Prevention (CDC) in Atlanta.

Beyond mainland China, Hong Kong has thus far borne the brunt of the outbreak, with at least 10 deaths among 286 cases. Epidemiologists have traced many of the other infections to a man who was hospitalized on Feb. 26 in Hanoi, Vietnam, after traveling from mainland China via Hong Kong. Several doctors who treated that patient later became ill. From Hanoi and Hong Kong, infected people traveling by airplane spread the disease to Europe, North America, other parts of Asia, and possibly Australia. At least 40 suspected cases have been identified in the United States.

Infections have occurred primarily through close and prolonged contact with sick individuals, WHO officials say. From 2 to 7 days after being exposed, an infected person suddenly develops a high fever and other flulike symptoms and suffers difficulty breathing. In some cases, respiratory problems are so severe that patients need artificial ventilators.

WHO, CDC, and numerous national health agencies have deployed teams of disease investigators and laboratory scientists to identify the pathogen and develop means to contain the outbreak. Investigators, who initially examined tissues from infected people for known viruses, bacteria, and other pathogens, suggest that a novel pathogen lies behind the epidemic.

Two candidate viruses had been identified by press time, one belonging to the paramyxovirus family and one to the coronavirus family. Paramyxoviruses produce well-known contagions such as measles and mumps. That family also includes the rare Nipah and Hendra viruses, both of which were discovered in the past decade after they emerged as deadly infections. Some coronaviruses commonly cause minor colds in people, but none has previously been linked to an outbreak as serious as the current one.