Chinese health authorities have begun tracing passengers who may have traveled in the same train carriage as a man who was reported Monday to be the mainland's fourth suspected case of A/H1N1 flu.

The man, with the surname Yang, returned to China's mainland on Friday from a tour of the United States and Canada, according to a notice from the Ministry of Health.

Yang returned to the southern coastal province of Guangdong by train Friday afternoon after flying into Hong Kong via the Republic of Korea Wednesday, said a ministry official.

Guangdong Provincial Center for Disease Control and Prevention confirmed Monday that Yang caught Korean Air flight KE020 from Seattle last Tuesday to Seoul, where he transferred to Korean Air flight KE607 to Hong Kong on Wednesday.

Guangdong Provincial Health Department said Monday Yang was admitted to the No. 8 People's Hospital of Guangzhou on Friday afternoon.

Yang, 59, and native of Guangzhou, the provincial capital of Guangdong, lives in Nanhai, a city in Guangdong. In late April, he joined an independent tour group visiting Canada and the United States.

Yang's itinerary in Canada and the United States, as well as Hong Kong is not immediately known.

According to the Guangdong Provincial Health Department, he developed a sore throat, blocked nose, and coughing on Thursday. He caught the T810 two-hour train service in Hong Kong at 4:35 PM Friday, in carriage No. 7, and returned to Guangzhou.

Yang's temperature tested normal when he boarded the train, but he developed a fever halfway through the journey. He was taken to the No. 8 People's Hospital for isolation and medical treatment, said the provincial health authorities.

Experts from Guangdong Provincial Bureau of Quality Supervision, Inspection and Quarantine, and Guangdong provincial and Guangzhou city centers for disease control and prevention conducted laboratory tests Sunday, and the result was A/H1N1 positive. Guangdong Provincial Health Department had the tests double-checked the same day and concluded he was suspected of having contracted A/H1N1.

The provincial health authorities are seeking passengers and railway staff who were in the same train carriage in which Yang traveled in order to quarantine them.

If the diagnosis is confirmed, he would become the fourth known case of the flu on the Chinese mainland. The other three were in Chengdu (Sichuan Province), Jinan (Shandong Province) and Beijing.

(Xinhua News Agency May 18, 2009)