Parents in a suburb of Cardiff have been contacted by health experts after a childminder and four children were diagnosed with tuberculosis.
All those affected attended a family centre in the Ely area of Cardiff
Another six people are being treated with preventative medicine but have shown no signs of TB.
The National Public Health Service for Wales said the woman was diagnosed in mid April and is "responding well" to treatment.
All those affected attended a family centre in the Ely area of the city.
The National Public Health Service for Wales (NPHS) said it had worked with Cardiff and Vale NHS Trust to investigate everyone who has been in contact with the woman.
Gwen Lowe, consultant in communicable disease control with the NPHS, said: "As a result of the screening we have carried out, we have detected a number of cases of TB.
"Careful assessment has identified that we should screen young children, childminders and adults attending a specific two-hour weekly drop-in session at the Ely Family Centre.
"Although it is unlikely that TB could have been transmitted in such a short time, we are offering screening tests as a precautionary measure.
"We are contacting staff and the parents or guardians of the children concerned."
The NPHS said the woman was diagnosed in mid April and is "responding well" to treatment.
A total of 11 adults and 30 children have been invited to be tested for TB on 6 June.
Dr Lowe added: "Other staff and visitors to the centre are at extremely low risk and do not need screening.
"Normal casual contact such as passing someone in a corridor or sharing a lift does not put someone at risk of developing TB."
Tuberculosis is an infectious disease caused by bacteria and is usually found in the lungs, although other parts of the body can be affected.
It is treated by a combination of antibiotics.