All schools in Greece have been closed
Three Greeks have died and another 36 are being treated following the spread of a flu-like virus that affects breathing.
The Greek Ministry of Health and Welfare confirmed there was an outbreak of pericarditis - an inflammation of the sac around the heart - since the beginning of March.
Officials added that Greek authorities had said there was no need to panic.
A spokeswoman said no Britons had been reported to have contracted the virus.
Travel advice
In a travel advice statement on the Foreign Office website, it said: "The health minister and special infections control centre of the Greek Ministry of Health have stressed that these are preventative measures and that there is no need for panic.
"They stressed that good personal hygiene and the frequent washing of hands were the best course of action."
It also advises travellers to ensure they have a E111 health form, available from post offices, and to take out travel insurance.
Greek authorities closed schools on Thursday, two days in advance of the planned start of the Greek Orthodox Easter break.
Officials said it was purely a preventative measure to stop cross infection.
Pericarditis causes pains to the chest, left side of the neck, shoulder, back and abdomen.
Breathlessness and swelling of the abdomen are also common symptoms.