Posters aimed at people with symptoms of the deadly virus Ebola are to be displayed outside hospitals in Swansea, Bridgend and Port Talbot.
The bright red and orange posters warn people not to enter the hospital if they have Ebola-type symptoms, including a fever, and have recently visited West Africa.
The posters are believed to be among the first of their kind in the UK as part of urgent measures to prevent the virus spreading.
A spokesperson for Abertawe Bro Morgannwg University Health Board said: "Anyone who fits the criteria is being asked to ring an intercom at the entrance first, instead of walking directly into hospitals.
"A member of staff will then come to the patient directly to help them."
A person in Cardiff is being monitored by Public Health Wales following possible exposure to the Ebola virus in West Africa.
The individual will be monitored for the duration of the incubation period of 21 days.