One of them is an American from California who was picked up for higher-than-normal temperature by thermal screening at Changi Airport. The other is a local resident who had a travel history to the United States and flu-like symptoms, who presented himself at a polyclinic and was referred to the CDC.

'Preliminary tests for Influenza A for both were negative,' said a joint statement from the Ministry of Health and Civil Aviation Authority of Singapore (CASS) on Monday night.

It said all healthcare institutions here have stepped up their infectious disease control measures to handle cases turning up at their hospitals, and there are no cases of human swine flu in Singapore, adding that 'MOH is monitoring the situation closely and will update the public should there be any new developments.'

As 'a good practice', the statement said some hospitals have advised their staff in critical areas such as the Emergency Departments (EDs) and Intensive Care Units to don full Personal Protective Equipment (PPE), which includes mask and gowns.

'There is a system of triage in the EDs where symptomatic patients with a travel history to affected areas, or contact with such persons, will be isolated within the hospitals. At the outpatient setting, for example, at GPs, polyclinics and TCM clinics, there is also a system where such cases will be referred to TTSH ED for further assessment,' said the statement.

As part of national level measures, the CAAS implemented precautionary measures at Singapore Changi Airport on Sunday night. Thermal scanners have been deployed at the Arrival Halls to measure the temperature of passengers just before they undergo immigration checks.

'These precautionary checks are non-intrusive and have no impact on the time needed by passengers to clear the various airport processes. Flights in and out of Changi Airport are continuing as normal,' said the statement.

'Passengers with a higher-than-normal temperature will undergo a more thorough medical assessment. If the doctor-on-duty ascertains the passenger requires further testing, the passenger will be conveyed to the CDC.'

The authorities advised members of the public to postpone or avoid non-essential travel to Mexico. In the event that travel to Mexico is unavoidable, the public is advised to take precautionary measures such as avoiding crowded areas, coming into contact with sick persons and maintaining high standards of personal hygiene at all times.

Members of the public are also advised to seek immediate medical attention if they develop symptoms of swine flu within seven days of travel to California, Texas, Kansas, New York City and Ohio in USA or to Mexico. They should also disclose their travel histories to their doctors.

MOH also advised hospital visitors to limit or postpone their trips to the hospitals where possible. The public should also maintain high standards of personal hygiene, such as washing hands frequently with soap and water, especially after contact with respiratory secretions like after sneezing and coughing. Those who are sick with respiratory illnesses should avoid crowded areas and wear masks if possible.