China and the World Health Organisation are at loggerheads over the interpretation of the fall in the number of reported new cases of Severe Acute Respiratory Syndrome in the world's most populated country and the epicentre of the disease.

"SARS is still present in China, and WHO continues to regard China as the epicentre of SARS," Executive Director for Communicable diseases at WHO, David Heymann said on Wednesday.

"It is our job, together with Chinese authorities, to try to prevent this disease from becoming permanently established in such a vast country," Heymann said as China's Health Ministry on Wednesday claimed the lowest figure of SARS since April 20 -- zero new cases and zero new deaths -- during the last 24 hours.

China's top SARS expert, Zhong Nanshan said that SARS diagnosis in China was generally accurate and the misdiagnosis rate was very low.

Zhong, Director of Guangzhou institute of respiratory diseases who has been fighting SARS since late last year, suggested that the disease's death rate of 15 per cent as estimated by the WHO might have been an 'overestimation'.

The daily number of reported new probable cases of SARS in mainland China has declined considerably in recent weeks, from an average of 166 cases during the first week of May, to 90 cases during the second week, 27 cases in the third week, and 16 in the fourth week.

The next few months will prove crucial in the attempt to contain SARS worldwide, which now greatly depends on whether the disease can be controlled in China, the WHO said. 

It said the resurgence of SARS cases in Toronto demonstrates how difficult it can be to maintain control over a new disease characterised by many puzzling etiological (the cause or origin of a disease or disorder as determined by medical diagnosis) and clinical features.

"Otherwise, cases in China, with its long porous borders and large migrant populations, could lead to outbreaks elsewhere and would thus make SARS a continuing threat for the rest of the world," it said.

Although great improvements in surveillance, reporting, infection control, and public awareness have occurred in China in recent weeks, WHO remains concerned about the sensitivity of case detection in some provinces and about the capacity of the health infrastructure to cope with a challenge on the scale of SARS.

Zhong questioned the contention of WHO experts, who said that estimates of a three to four per cent death rate made at the early stages of the outbreak was 'too optimistic', and believed the rate should be 14 to 15 per cent.

WHO has made its estimation mainly based on data from Canada and Singapore, where the SARS death rate was 'indeed very high', Zhong said.

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