Imported cases raise increasing concerns

Asymptomatic group

By contrast, one development that is causing greater concern has been asymptomatic groups testing positive for the virus while exhibiting no symptoms.

The locally transmitted case added on Saturday has illustrated the danger of these carriers. The female patient in Luoyang, Henan province, is believed to have come into contact with a doctor on March 21, and the two then shared a vehicle and dined together. The doctor tested positive for the virus during an organized health check on Wednesday and was classified as an asymptomatic case, according to the provincial health commission.

Both Chinese and World Health Organization experts have said that many asymptomatic individuals are detected when placed under medical observation as close contacts of confirmed cases.

Even though scientists are still working on pinning down the true proportion of asymptomatic individuals, Zhong Nanshan said the epidemic's curve and the current mortality rate suggested that the number of undetected, symptom-free individuals is unlikely to be large in China.

However, Zhong, and the many other health experts, are not downplaying the challenge.

Zhou Wenting in Shanghai contributed to this story.