Public Health Wales says it is notified of around 200 cases of TB each year in Wales.
It says it is "very rare" for tuberculosis to be transmitted within a school environment, and screening is being offered to pupils as a "precaution."
We are emphasising to pupils, parents and staff that it is very rare for TB to be transmitted within a school environment and so we are offering screening as a precaution.
Close contact with an infectious individual over a long time period, such as living in the same household, is usually required for a person to become infected with TB.
The infection is difficult to catch but treatable with antibiotics.
Other close contacts of the person who has been unwell have already been traced. Another four cases of TB have been identified in the Llanelli area over the last year, but none of these have links to the school.
Investigations into these cases are continuing with the involvement of Hywel Dda Health Board with treatment, advice and screening offered where appropriate.
More top news
Conner Marshall, 18, died after a 'vicious and unprovoked attack' in Porthcawl in 2015.
A new campaign is being launched to tackle arson in Wrexham following a number of attacks in the area.
ITV Wales can reveal thousands of patients have waited over an hour for an ambulance since the 'amber' category was introduced last year