Currently, experts at the Beijing-based Chinese Center for Disease Control and Prevention are doing laboratory work in order to discover exactly which virus caused the outbreak, Li Liming, director of the center, told the press Thursday afternoon.

Liang Guodong, a viral disease expert with the center, said they suspected viral pneumonia was the culprit since many patients were doctors and nurses, who had close contact with other patients.

Liang returned from Guangdong, where he had been sent by the Ministry of Health as a member of an investigation team.

Health experts called the illness "atypical pneumonia" because it was not caused by pneumococcus, which leads to normal pneumonia. Atypical pneumonia can have 17 different causes such as virus, bacteria or mycoplasma, said Dr. Zhao Mingwu with the No. 3 Hospital of the Medical School of Peking University.

The experts have excluded the possibility that the illness was caused by the plague, anthrax, haemorrhage fever or leptospirosis, which had been rumored to be causes.

Patients suffered acute symptoms including high fever, dry cough, muscle pain and weakness when they were hospitalized. But now many have recovered and left hospitals, Li said.

No new cases have been discovered for four successive days in Guangdong, which neighbors Hong Kong.

"The situation is under control and is stable. It is not as serious as the rumors say," Li said, but Li stressed that the nation's disease control institutions remained on high alert and were keeping a close eye on the epidemic.

Li's center also maintained good communication with health departments in Hong Kong and Macao, where the illness has been the top concern in recent days.

The outbreak in Guangdong has aroused concerns nationwide since unconfirmed news and rumors were disseminated via the Internet and short messages on mobile phones.

Panic also prompted the craze to purchase traditional herbal medicines, vinegar and surgical masks, which people believed could keep the illness away.

But the experts in the center clarified that there was no evidence that herbal medicines and vinegar could effectively block the virus, and some exaggerated news reports have caused unnecessary panic.

The center has suggested some preventative measures such as improving ventilation in offices and homes, disinfecting the air in hospitals, avoiding large crowds, wearing masks when in contact with patients, keeping warm, and consulting a doctor when experiencing suspicious symptoms.

(Xinhua News Agency February 14, 2003)