May 23, 2003

WASHINGTON (AP) -- SARS could become a global epidemic if there were no efforts to control it, but vigorous public health measures can keep the virus from spreading and minimize the number of people infected, according to two studies.

Researchers writing in the journal Science said the virus that causes severe acute respiratory syndrome is sufficiently contagious to spread around the world if left unchecked. But they concluded the killer disease will yield to rigorous public health measures such as quarantine and early treatment.

Two research teams used mathematical models to predict the course of the SARS outbreak. The two studies were rushed into print by Science and were released on Friday by the journal.

One research team, from the United States and Canada, found that a combination of early detection, quarantine and a reduction in the infectiousness of each patient would significantly slow the public spread of the disease.

A second team, composed of United Kingdom and Hong Kong specialists, focused on the disease spread in Hong Kong.

"We show that the number of infectious individuals in Hong Kong is much smaller now than at previous points during the epidemic," team leader Steven Riley of the Imperial College in London said in a statement. "The risk to visitors to Hong Kong from SARS is much reduced although not yet zero."

The U.S.-Canadian team estimated that each case of SARS would cause 2.2 to 3.6 additional cases if there were no public health control efforts. The study by Riley and his team found that each case in Hong Kong triggered two to three new cases on average at the beginning of the epidemic.

More than 8,000 people worldwide have been infected with SARS and at least 689 have died. The majority of the victims are in China and Hong Kong.

The spread of the disease has slowed and the World Health Organization on Friday lifted advisories that had discouraged travel to Hong Kong and the Chinese province of Guangdong.

The U.S.-Canadian study, with Marc Lipsitch of the Harvard School of Public Health as first author, said the future effect of SARS, which is caused by a new, little-understood virus, is still uncertain. Its impact on international public health in the future, they said, will depend on such factors as how long survivors of the infection retain natural immunity, the effect of seasonal changes on transmission rates, and whether the virus can live in other animals. If the virus can live in other animals, this forms a reservoir from which the disease can spread to humans in the future.

"These uncertainties make long-term forecasting of the course of the epidemic premature," the authors said in Science.

In the Hong Kong study, the researchers said that the epidemic is now in decline, but warned that "continued vigilance is necessary for this to be maintained."

Copyright 2003 The Associated Press. All rights reserved.