Two people are being treated in Scotland for the potentially deadly diphtheria infection.
NHS Lothian has confirmed the two cases are related and both patients are thought to be in hospital in Edinburgh.
The health board said those involved had recently returned from overseas.
Public health experts said the likelihood of any additional cases was very small, as most people were protected by immunisation given in childhood.
In Lothian, 98% of children are vaccinated against diphtheria by the age of 24 months.
Alison McCallum, director of public health for NHS Lothian, said: "All close contacts of these patients have been identified, contacted and followed up in line with nationally agreed guidelines.
"We encourage people travelling abroad to visit Fit for Travel where they can access information on how to stay safe and healthy abroad, as well as destination specific health advice."
What is diphtheria?
Diphtheria is a highly contagious and potentially fatal infection that can affect the nose and throat, and sometimes the skin.
It can lead to difficulty breathing, heart failure and paralysis.
The infection is spread by coughs and sneezes, or by sharing items such as cups, cutlery, clothes or bedding with an infected person.
It is rare in the UK, because babies and children are routinely vaccinated against it.
There is a small risk of catching the disease while travelling in some parts of the world.