All 98 people who had close contact with a suspected human case of bird flu in south China have tested clear of the disease, the local health bureau on Thursday.

The contacts included relatives of the patient, a 31-year-old man surnamed Jiang, medical workers in a local clinic and in Shenzhen People's Hospital, where Jiang had been treated, and the patients in the same ward.

Tests on the 98 contacts all proved negative for the H5N1 strain of the bird flu virus, but doctors would continue observations of them, according to the health bureau of Shenzhen, a city in Guangdong Province.

A bureau source said Jiang was still in a critical condition and being treated in Donghu Hospital in the city.

A test sample from Jiang had been sent to Beijing for verification by the Ministry of Health.

Jiang started to show symptoms of back pain, fever and a cough on June 3. He was admitted to the Shenzhen People's Hospital on June 9.

The Shenzhen Center of Disease Control conducted tests for the H5N1 virus. The Guangdong provincial health bureau immediately reported the case to the Ministry of Health for verification.

The patient was transferred to Donghu Hospital on Tuesday for advanced treatment.

Shenzhen city government has announced a second-degree emergency as a precaution against bird flu in the city.

Medical staff are disinfecting all possible contaminated places.

Jiang, a truck driver, had no contacts with birds before becoming ill. However, his wife bought a freshly slaughtered chicken from a local market two weeks ago, and cooked it for dinner for five family members, including Jiang.

None of Jiang's family showed similar symptoms. They and other close contacts are under medical observation.

He would become China's 19th reported human case if he is confirmed as having the H5N1 strain of bird flu.

China has reported 18 human cases, involving 12 deaths.

According to the World Health Organization, 225 human bird flu cases have been confirmed since late 2003, involving 128 fatalities.

Editor: Yan