Three US-Cambodians have tested negative for the H1N1 virus, after they shared an international flight where one passenger was found to have the illness, health officials said Monday.

Sok Touch, director of Health Ministry’s communicable disease control department, said Chay Cerone, 62, was found in Battambang province, while Pann Thy, 46, and Pann Saroun, 26, were found in Kampot province.

All three tested negative for the virus, which appeared in Mexico last month and has sparked concerns of a pandemic. They were tested by the Pasteur Institute in Phnom Penh.

Authorities began searching for the three visitors when South Korea issued an alert saying that one passenger on a May 17 flight from Seattle to Incheon had tested positive for the illness.

Cambodia has no known cases of the H1N1 flu, but officials say they remain vigilant.

Chhour Kimny, chief of immigration police at Phnom Penh International Airport, said his personnel continue to watch for travelers with flu-like symptoms.

Between 1,300 and 1,500 passengers have been investigated through temperature scanners, which were installed at both international airports a few days after the first reported outbreak of the H1N1 flue was reported from Mexico.

The World Health Organization says 43 countries have officially reported more than 12,000 cases of infection, which has caused 86 deaths worldwide.