New suspected cases were reported Sunday in the city of Yongkang, in Zhejiang Province; Yichang, in Hubei; Chenggong County, Yunnan; Pingyu County, Henan Province; and a division of the Xinjiang Production and Construction Corp in the Xinjiang Uygur Autonomous Region.

On Saturday Ezhou of Hubei Province and Chao'an County of Guangdong Province also reported the virus.

The World Health Organization (WHO) said China's window of opportunity to stop the spread of the disease is narrowing, though there have been no human cases.

It has been almost a week since the first confirmed the presence of H5N1 avian influenza, or bird flu, in poultry in South China's Guangxi Zhuang Autonomous Region. Such cases were also reported in Hunan and Anhui provinces.

So far, there are no known human cases of H5N1 avian influenza in China, said Ministry of Health spokesman Mao Qun'an.

A report yesterday of a possible human case in Shanghai was discounted by China's Ministry of Health, said the WHO's Beijing office yesterday.

President Hu Jintao, on a state visit to Egypt, said on Saturday China has full confidence in its ability to tackle the problem and in preventing the disease from spreading.

The Chinese mainland has been culling poultry within three kilometers of infected farms and vaccinating poultry within five kilometers.

Measures also include a ban on exports of poultry and poultry products from affected areas, closure of poultry markets and strengthening quarantine requirements of the residents from affected areas.

The State Council has established a National Bird Flu Prevention Headquarters in an effort to intensify prevention and control work on bird flu, and Vice-Premier Hui Liangyu was appointed director-general of the headquarters.

However, with more outbreaks reported daily, the mainland's window of opportunity to contain the spread appears to be getting smaller, said WHO spokesman Roy Wadia.

The greater the number of cases, the bigger the challenge, especially given the mainland's size and the geographical spread of poultry populations.

One of China's main weapons against the influenza spread is speed.

When the disease breaks in a new place, culling poultry, isolation and quarantines are quickly imposed, said Mao Qun'an of the Ministry of Health.

Still, the WHO has raised concerns over the environmental impact of the bird culls and urged people involved "take suitable safety precautions" to help prevent the possibility that these people might be infected.

In Hong Kong, local officials are also taking measures to ensure poultry retailers observe the law.

So far, there have been several cases reported in Viet Nam and Thailand of bird to human transmission of H5N1 avian influenza.

While there are no confirmed cases of human to human transmission, the World Health Organization said Sunday that two sisters who died of bird flu in Viet Nam may have caught the disease from their brother. That may prove to be the first known case of human-to-human transmission of the lethal virus.

"The investigation has not been able to conclusively identify the source of infection for the two sisters," the WHO said in a statement. "However, WHO considers that limited human-to-human transmission, from the brother to his sisters, is one possible explanation," it said.

According to an analysis from experts at the centre for Disease Control and Prevention in Atlanta, the United States, human-to-human contact is not farfetched.

If a person already infected with common human flu contracts the bird flu virus, the two could link.

Should that happen, the bird flu virus may combine with human flu virus and gain the ability to spread among humans.

People do not have a natural immunity to H5N1. That's what makes the scenario of human-to-human transmission so dangerous, said Roy.

Still, the H5N1 virus must face several hurdles before it can mutate, Roy added.

At the same time, WHO refuted claims that bird flu virus originated from China.

There is no evidence to support the claims that China is the source of the bird flu virus, and there is no clear answer yet as to where the virus originated, WHO spokeswoman Fadela Chaib was quoted as saying.

(China Daily February 2, 2004)