Four samples are being tested in Ireland in connection with the swine flu virus.
Dr William Hall, Chairman of the Pandemic Expert Group, said one sample had been tested last night and proved negative.
He said the public would be informed if and when any case proves positive over the coming days and weeks.
In New York, the World Health Organisation has raised its alert level for the outbreak from level three to level four.
In Scotland, two people admitted to hospital after travelling to Mexico have been confirmed as the first cases of swine flu in Britain.
The two flew back to Scotland last week after a holiday in Mexico and are being treated in Monklands hospital in Airdrie, near Glasgow.
Scottish Health Minister Nicola Sturgeon said that the two patients were 'recovering well'.
Seven other people who came into contact with them, among 22 tested, have developed mild symptoms of the flu, she said.
British health minister Alan Johnson said earlier that the UK was implementing ‘enhanced’ health checks at entry points into the country to identify passengers arriving with symptoms of the illness.
Meanwhile, the death toll in Mexico from an outbreak of a new type of swine flu has risen to 103 people.
Cases of the AH1N1 strain of flu have now been confirmed in the US, Britain, Canada and Spain, and suspected cases in New Zealand, France, Italy and Israel.
But the WHO emphasised that it is not making any recommendation againmst travel, or for closing borders.
Mexican Health Minister Jose Angel Cordova said this afternoon that up to 149 deaths are now thought to be 'possibly' swine flud related.
He announced that all schools in the country are to be closed until 6 May.
But he earlier said that out of around 1,600 suspected cases, only 400 people have so far been hospitalised.
'The most recent reports we have are of 1,614 cases, with 103 deaths, and we still have around 400 patients in hospital,' Mr Cordova said, explaining that around two-thirds of the sick patients had recovered.
The outbreak of a new strain of flu in Mexico in the last few days has stoked fears of a global epidemic as new cases crop up in the US and Canada.
Many Mexicans stayed indoors at the weekend or ventured out wearing surgical masks, especially in Mexico City where the government stopped public events and closed museums, bars and stadiums to try to contain the virus.
The World Bank has said that it is providing Mexico with more than $200m in loans to help it deal with the outbreak.
The Spanish government said the country's first case of swine flu had been confirmed in a man recently returned from Mexico.
It was the first recorded case in Europe of the outbreak.
The EU has called a meeting for Thursday to evaluate the threat posed by the outbreak.
EU Health Commissioner Androulla Vassiliou has also recommended avoiding non-essential travel to areas hit by the swine flu outbreak.
Passengers landing at Heathrow Airport on flights from Mexico are being questioned about possible symptoms before being allowed to get off.
Speaking on RTÉ's Morning Ireland, chief medical officer of the Department of Health Dr Tony Holohan said the country was well-prepared if swine flu hits Ireland, with enough anti-viral drugs to cover half the population.
The Health Service Executive is advising anyone from Ireland who has recently returned from Mexico, California or Texas (within seven days), and develops an influenza-like illness, to phone their family doctor for advice.
The US State Department has issued a travel warning urging Americans to avoid all ‘non-essential’ travel to Mexico because of the outbreak.
Possible infections are also being checked in Israel and New Zealand.
Australia will introduce airport checks for swine flu and has alerted hospital emergency wards and doctors to be on the lookout for the virus.