Epidemiological experts have attributed the steady decline in the cases of severe acute respiratory syndrome (SARS) on the Chinese mainland to its effective prevention and control measures.

"With detailed analysis of the onset date of SARS cases, we see that the downward trend of the epidemic was closely linked with the prevention and control efforts that we have resorted to," said prestigious epidemiological expert Xu Dezhong.

According to the World Health Organization (WHO), the average incubation period for SARS virus was five days and the longest reached 10 days.

"The data change occurring five and 10 days after the measures could show whether they had worked or not," said Xu.

Analysis of the onset date of SARS cases on the Chinese mainland showed that the numbers, after reaching a climax between April 23 and 25, began to drop on April 26 and then slumped on April 30.

"That showed clearly that the decline of the epidemic was directly connected with the measures we've been taken since April 20," Xu said.

Stringent implementation of the Ministry of Health (MOH) case definition had also helped contain the infection, acknowledged experts.

Rao Keqin, a noted epidemic analyst from the MOH, said that case definition, which has been revised by the MOH twice in the past month, had a broader definition for suspect SARS cases, but was very strict in terms of discharging cured patients from hospitals.

"The MOH definition is more appropriate in terms of China's true situation, and it is more strict and safer than the World Health Organization (WHO) definition," said Rao.

"The definition helps make accurate diagnoses and prevents any suspected patient from being neglected."

The definition used by the WHO did not identify as suspect or probable SARS cases patients who had no SARS contact history, added Rao.

"The MOH definition also requires the cured SARS patients to beput under medical observation in hospital until they are perfectlyrecovered."

The experts have also denied that the SARS epidemic has a natural declining tendency.

"The virulence of some epidemic agents could weaken gradually,"Rao noted. "But it does not weaken in a matter of several months, but rather in several years or even longer."

In addition, medical studies showed that SARS epidemic is quitedifferent from other deadly infectious diseases, and there is no apparent evidence that the virulence of its agent naturally weakens, said Rao.

"So the falling in the number of SARS cases on the Chinese mainland was clearly due to the prompt and effective prevention measures taken rather than anything else," he said.

MOH figures showed that the number of SARS cases in Beijing rose and then dropped dramatically. From 10:00 a.m. May 20 to 10:00 a.m. May 21, Beijing reported eight new SARS cases.

Experts predicted that the SARS epidemic in Beijing could be curtailed at a basic level at the end of May or the beginning of June.

"New SARS cases would be reported only at the one-digit level at that time and possibly there would be zero new SARS case reported on some days," said Rao.

But Rao warned that there might be some fluctuations of the SARS disease since a vaccine hasn't been found and there are no distinct control measures for this disease.

"Sporadic cases would remain for a certain period of time or rather a long period," noted Rao, but "an outbreak like the one atend of April will not occur under the strict and tight prevention measures."

Experts also warned the public not to let up on prevention measures.

"With the resumption of business operations and students returning to schools and migrant workers to the cities, there is still a great deal of arduous work to do to control the SARS spread," said Xu Dezhong.

"The war on SARS has just achieved temporary results, not final,so we should go on with our prevention measures for a rather long time," he said.

Meanwhile, experts suggested the general public continue payingattention to personal hygiene, hand washing and wearing face masksin crowded areas.

"The public should continue to be alert to those people runninga fever or having other SARS symptoms," said the experts. "The principles of early reporting and early treatment should still be followed earnestly."

Editor: Liao Ming