Doctors have lifted the quarantine Wednesday for an A/H1N1 flu patient in southern China in the mainland's first serious case.

However, the 17-year-old boy is still in a coma and suffering severe brain edema. He is hospitalized in the ICU ward of the Guangzhou Municipal Institute of Respiratory Disease, said Xiao Zhenglun, professor from the institute, Wednesday.

The quarantine was lifted after tests showed he was negative for A/H1N1 for three consecutive days since last Saturday.

The boy, a high school student in Guangzhou, capital of Guangdong Province, developed a fever on Aug. 5, and passed out the next day at home before being hospitalized.

Xiao said doctors in the institute have found evidence that the patient suffers a rare genetic disease called Brugada Syndrome, which is believed to have caused his critical condition.

The Brugada syndrome, not known to the patient and his parents beforehand, was discovered through abnormal electrocardiogram findings. The disease may cause cardiac arrest.

The doctor said the disease might have been triggered when the patient had a fever, resulting in arrhythmia, ventricular fibrillation and sudden cardiac arrest, which were exactly the patient's symptoms when he was sent to the hospital.

The Chinese mainland had confirmed 2,729 cases of A/H1N1 flu as of 5 p.m. Monday, the Ministry of Health said.

Of confirmed A/H1N1 cases, 2,396 have recovered and discharged.

Previously there had been no fatal or critical cases resulting from A/H1N1 reported on the Chinese mainland, but one infected patient in Hangzhou from eastern Zhejiang Province reportedly died of electrocution in a ward lavatory on July 1.

(Xinhua News Agency August 19, 2009)