Two people are being treated for diphtheria following their returns to Scotland from trips abroad.
NHS Lothian confirmed the related cases on Saturday, adding those who have been in close contact with the patients have been identified and contacted.
It is believed the pair are currently receiving treatment at a hospital in Edinburgh.
Diphtheria is a highly contagious and potentially fatal infection.
It can affect the nose and throat, and sometimes the skin.
The infection is rare in the UK but there is a small risk of contracting it while travelling in some parts of the world.
Alison McCallum, director of public health and health policy at NHS Lothian, said the likelihood of any additional cases is small.
She said: "Two related cases of diphtheria have been confirmed in the Lothian area, with both patients having recently returned from abroad.
"All close contacts of these patients have been identified, contacted and followed up in line with nationally agreed guidelines.
"The likelihood of any additional cases is very small, as most people are protected by immunisation given in childhood.
"In Lothian, 98 per cent of children are vaccinated against diphtheria by the age of 24 months.
"We encourage people travelling abroad to visit (the website) Fit for Travel, where they can access information on how to stay safe and healthy abroad, as well as destination-specific health advice."
