The student from the Llanishen Fach center in Rhiwbina developed symptoms on Thursday and was self-insulating.
Cardiff’s council did not say that other students or staff had developed symptoms.
The student isolated himself at home before getting tested for the virus on Monday, which was confirmed positive on Tuesday.
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A board spokesperson said, “Due to the expected increase in the rate of community transmission of the virus, a number of measures are in place to reduce the risk to students, staff and families who attend all of our centers.
“These measures include robust cleaning programs implemented throughout the school day with an emphasis on regular cleaning of frequently touched surfaces.
“The implementation of social isolation guidelines and high standards of personal hygiene are followed, including regular hand washing and the use of a hand sanitizer.
“” The board would like to reassure everyone, in this difficult time, that we are taking all necessary measures to guarantee that the risk of transmission within school clusters is reduced to the lowest possible level. “
The board stated that if a family member living in the same household as a student has symptoms or a positive test for Covid-19, then the student must self-isolate immediately for 14 days before reintegrating the center.
They added that if the student showed symptoms of the virus himself during the 14-day isolation period, another seven days of isolation should be started at the onset of symptoms.
Any student with positive symptoms or tests should self-isolate immediately for at least seven days or as long as symptoms persist, before returning to the center.