About 100 children will be offered screening for tuberculosis after a member of staff at a nursery in Cardiff was diagnosed with the infection.
Letters have been sent to parents of children attending the Daisy day nursery in Llanishen.
Staff and close contacts of the patient will also be offered the screening when it takes place in September.
Daisy has a second day nursery in the Barry area, but there is no risk to children who attend that premises.
TB is usually found in the lungs but any part of the body can be affected.
Anyone can catch TB by breathing in the bacteria in tiny droplets sneezed or coughed out by someone who has TB in their lungs.
Dr Gwen Lowe, consultant in communicable disease control for Public Health Wales, said: "The infection is difficult to catch but easy to treat with antibiotics."