Fifteen positive cases of Covid-19 have been detected following a programme of mass testing in Kilkeel, Co Down.
However, public health experts say that it could take several days to determine if the Delta variant is present.
More than 1,000 tests were carried out in the area over the weekend.
The testing of asymptomatic people in targeted neighbourhoods began after a small number of "probable" cases of the Delta variant of the virus, which was originally detected in India, were found.
It was done in advance of confirmation as to whether or not the new variant is present, so that public health experts can identify asymptomatic cases early and try to reduce the risk of a wider spread in the community.
Dr Bríd Farrell from the Public Health Agency said that the positive test results are now being further examined to see if the Delta variant is present.
She said: "All positive test results are now being assessed for a preliminary indication of whether a variant is present or not and then submitted for whole-genome sequencing to confirm the type of variant. This process can take several days to complete."
The public health agency in Northern Ireland said that all of the positive cases have been advised to self-isolate and that "robust" contact tracing has been carried out.
Three mobile testing units will remain in Kilkeel to accommodate anyone in the identified areas who have yet to be tested.
The Public Health Agency said that a number of the positive cases have been linked to Kilkeel High School and that all staff and pupils there will be tested "as a precautionary measure".
Dr Farrell said that this is a "timely reminder" to everyone in Northern Ireland to keep up all the public health measures to stop the spread of Covid-19.
She added: "Continue with good hand and respiratory hygiene, keep your distance of 2m from others where possible, wear a face-covering where necessary, keep rooms well ventilated, and if you're offered the vaccine, book your appointment. Stopping the spread of the virus will help save lives."