Two men and three women who flew in from the United States tested positive for the A/H1N1 virus in Hong Kong on Friday, bringing the total number of infection to 20 in the city, Hong Kong health authorities said.

The city's 16th confirmed case involves a 21-year-old woman who returned to Hong Kong from Los Angeles late on Thursday aboard flightCX881. She called the Center for Health Protection's (CHP) hotline after developing symptoms at home. She was sent to Princess Margaret Hospital by ambulance.

Another 21-year-old woman felt ill while still on the plane and was sent to Tuen Mun Hospital directly by port officers at the Hong Kong International Airport. She flew in from San Francisco on flight SQ1 on Friday morning.

The 18th confirmed patient is a 21-year-old man who flew in from New York via Seoul and arrived on May 26 aboard flight KE607.He fell ill on May 28 and took a taxi to North District Hospital.

The 19th and 20th cases involve a 24-year-old man and a 19-year- old woman who arrived from New York on flight CO099 on Wednesday evening.

The CHP will trace patients' family members and close contacts, as well as passengers who had been on the same flights, said Thomas Tsang, controller of the CHP.

As the number of imported cases increases, it won't be long before the first local case emerges in the city, said Gabriel Leung, under secretary for Food & Health.

He said if the first local case emerges in Hong Kong, primary schools, kindergartens, nurseries and pre-schools will suspend classes for 14 days and the government will decide whether to prolong any such suspensions.

The Hospital Authority's seven designated clinics will also be activated and the number of clinics will increase to 18 if there are many people seeking help.

All passengers arriving in Hong Kong will be required to complete a new health declaration form from June 1. The form requires travelers to fill in more information including their seat number on the flight, ship or vehicle, their destinations for the next seven days after arriving in Hong Kong and the transport to be used and contacts for those seven days.

(Xinhua News Agency May 30, 2009)