At least 37 people have been diagnosed with Covid-19 as a result of a karaoke party on the outskirts of Limavady, it can be revealed.
Meanwhile, more than 100 people have been told to self-isolate for 14 days after coming into contact with confirmed cases from the cluster.
Evidence suggests that it may take up to two weeks before a person falls ill with Covid-19 after coming into contact with the virus.
As a result the 14-day isolation period is a key component of Government efforts to stop the spread of the virus, as it significantly reduces the chance of people who may fall ill from passing Covid-19 on to others.
The figures have been released by the Public Health Agency (PHA) as details of Northern Ireland's coronavirus contact tracing app ate to be launched this week.
Stop Covid NI will supplement the phone-based contact tracing programme already in place and has the support of the Executive. Northern Ireland will be the first part of the UK to have a contact tracing app.
Health officials are working hard to prevent a second deadly surge of the virus, which has claimed more than 850 lives since it first arrived here. However, concerns have been raised about a lack of information over the location and extent of emerging clusters, particularly as shielding is due to be paused on Friday.
Health officials have provided some information to the public about clusters, but have so far only confirmed the location of the cluster arising from the karaoke party.
The PHA revealed that since the start of the Limavady cluster 37 cases have been added to the contact tracing database, while 140 contacts had been identified.
The PHA declined to provide any further information, stating that it may result in people being identified.
This is despite growing calls for clarity over the location of clusters to enable the public, particularly those most at risk from the virus, to take additional measures to protect themselves when it is active in their community.
Alliance Party MLA Paula Bradshaw, a member of the Stormont health committee, said: "I recognise the challenge for the PHA in ensuring that patient confidentiality is assured as part of the contact tracing process and we now have good evidence that contact tracing is fundamentally working in identifying and following up clusters.
"Nevertheless, in a public health emergency we must also have public information so that the public can make decisions about how to go about their daily lives safely.
"I would still wish to see more information about the locality of clusters immediately when they are identified, and about the nature of clusters in due course, so we can identify clearly what specific activities are leading to 'superspreading'."
Shielding is pausing on Friday for the 95,000 people who were warned their lives are at risk if they become ill with Covid-19.
They have received limited advice about what is safe from Friday, which includes a recommendation that they should continue to work from home where possible.
At the same time it has emerged that 16 clusters have been identified here since May 24, with more expected in the coming months.
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When Health Minister Robin Swann added Northern Ireland to the new quarantine rush job on Saturday night, he will not only have dismayed the many hundreds of local holidaymakers, whose present and future travel plans have been thrown into disarray, but also the hundreds of thousands involved in and dependent on the Spanish tourism industry.