Seven passengers who were on the same flight as a swine flu patient from the United States to Hong Kong on May 11 and then traveled to Taiwan on two Cathay Pacific flights were urged to contact health authorities on May 13.

"The seven passengers should contact health authorities as soon as possible because there is a possibility that they could have been exposed to the Influenza A (H1N1) virus," said Shih Wen-yi, spokesman for the Central Epidemic Command Center.

Shih issued the call after Hong Kong confirmed earlier in the day its second case of Influenza A (H1N1) infection, better known as swine flu.

The case involved a 24-year-old Hong Kong man who took Cathay Pacific Airways flight CX879 on May 11 from San Francisco to Hong Kong. Seven of the passengers aboard the same flight traveled to Taiwan later that day on two other Cathay Pacific flights.

Shih said the Hong Kong man has been quarantined at an airport clinic since his arrival in Hong Kong and is now in stable condition.

As none of the seven passengers who shared the flight with the patient were seated in the high-risk area -- the three rows in front of and behind the man's seat -- the epidemic command center has yet to decide whether they should be provided with preventive medication, Shih said.

"But we hope the seven passengers will immediately contact health authorities," added Shih, who is also deputy director-general of the Centers for Disease Control in Taiwan.

As the new swine flu virus is not as virulent as originally thought, Shih said, the epidemic center will review its current epidemic preventive measures.

Since the global swine flu outbreak, passengers who were on the same flights as Hong Kong's first confirmed case, Japan's first three confirmed cases and China's first confirmed cases were all required to have their throat secretions tested and to take preventive medication. None of them have tested positive for the virus.

Shih said the epidemic center may only ask those who were seated in the high-risk areas of the aircraft to undergo tests and take preventive medications. "A final decision will be made soon," he added.

To date, there have been no confirmed swine flu cases in Taiwan.