Chinese researchers searching for the causative agent of severe acute respiratory syndrome (SARS) have narrowed their focus to chlamydia-like agents.

Their on-going efforts to identify the causative agent have been integrated into a global network of laboratories racing to find the origin.

While scientists outside China have hypothesized that SARS is caused by a new virus belonging to the coronavirus family, Chinese scientists say they have obtained a great deal of evidence in support of their hypothesis.

"A new chlamydia-like agent or a mutation of chlamydia could very possibly be one of the causes of SARS," Prof. Li Liming, director of the Chinese Center for Disease Prevention and Control, told the press Friday afternoon.

He said the hypothesis was based on the results of observation under an electron microscope, tissue cultivation in labs, and serological studies carried out since February.

Since Feb. 18, researchers at Li's center have discovered chlamydia-like agents in five tissue samples taken from people who died of SARS.

Li said the tissue samples were taken in several different hospitals in different areas of the country.

"The agent is clearly similar to chlamydia, though not common chlamydia, which usually causes pneumonia, trachoma or ornithosis. We have thus decided to use the term "chlamydia-like agent," Li said.

He added that further research would be necessary, including experiments on lab animals and studies on more serum samples, before a final conclusion could be reached.

"We think it could be the cause, or one of the causes of SARS," Li said, although we haven't ruled out the possibility that other causes may exist."

Several of the experts from the Chinese disease prevention and control center are currently in Guangdong, accompanying a team of World Health Organization experts who are searching for clues to the origin of SARS.

The WHO said Friday that SARS "is thought to be caused by a new virus in the coronavirus family," though the exact identity of the virus has proved elusive.

Virologist Hong Tao, a member of the national disease prevention and control center, said they had detected traces of coronavirus from three tissue samples. However, the team has not conducted follow-up research because it does not consider it a research focus, Hong said.

The Chinese researchers have joined a WHO-initiated global network of laboratory experts and have exchanged their latest findings with their international colleagues through teleconferences.

Henk Bekedam, WHO representative in Beijing, said the international community should remain open-minded about the cause of SARS until a final conclusion is reached.

Most importantly, Chinese scientists have joined the global network of laboratory experts to share information to find the cause as soon as possible, Bekedam said. "We're very pleased (about it)."

(Xinhua News Agency April 5, 2003)