A total of 555 passengers entering China were found to have fever and acute respiratory symptoms in half a month, said the General Administration of Quality Supervision, Inspection and Quarantine on Monday.

Their cases have been handed to local health departments for further observation or treatment, the ministry said.

About 5.13 million passengers entering China were screened from April 25 to May 10, the ministry said.

The ministry has been quarantining planes, ships, trains, automobiles and other vehicles from the countries affected by outbreaks of A/H1N1 flu.

Passengers entering China have been required to fill out health declaration forms so that they could be effectively traced if any A/H1N1 flu cases were found among them, the ministry said.

A Chinese mainland male surnamed Bao, who recently returned from the United States, tested positive for A/H1N1 influenza, the first such case reported on the Chinese mainland, the Ministry of Health said on Monday.

Experts said A/H1N1 flu virus has an incubation period from two- to- seven days and patients would not show a fever, headache or cough in the incubation period. This makes it hard for infected passengers to be immediately detected.

(Xinhua News Agency May 12, 2009)