A single outbreak of Covid-19 among students in the west of Ireland has led to 442 further cases in more than 200 separate household outbreaks.
Health Service Executive West Public Health Director Dr Breda Smyth said the initial outbreak was "quite large".
She said it involved young adults aged between 16 and 24.
Up to the end of Wednesday, a total of 442 cases could be linked back to that single outbreak.
RTÉ reports that of those 442 cases, 179 were linked to multiple household clusters.
Of these, there were 20 clusters in total, ranging from two to 42 cases each.
At a press conference on Thursday, Dr Smyth said that in addition there were 145 cases linked to single household outbreaks, as well as another 118 cases confirmed.
A total of 224 households were affected from the initial outbreak.
The Irish Department of Health said on Thursday it had been notified of 39 further coronavirus-related deaths and 462 new cases across the country.
In a statement, the country's National Public Health Emergency Team said that 10 of the deaths occurred in March, 12 in February, 13 in January and three earlier than this.
There have been a total of 4,396 Covid-related deaths in the Republic, while the number of confirmed cases now stands at 221,649.
Restrictions in the Republic of Ireland are currently at their highest level.
Under Level 5 restrictions there is a ban on all household visits, non-essential retail is closed and there is a 5km limit on travel.
Dr Smyth said that as well as spreading infection in the community, there were knock-on effects in other areas, such as exposure to the virus, as well as transmission, in the hospitality and retail sectors.
She said that a further cluster of infection was recorded in another part of the country, which was linked to the initial outbreak.
Dr Smyth said the movement of the young people through the region as a result of socialisation was among the primary reasons for transmission, adding that house parties were also a factor.
She also provided details on the timeframe for how the virus spread from the first outbreak.
On day one of the outbreak, there were two clusters, four households and four cases confirmed.
On day two, this became six clusters, 12 households and 15 cases.
By the end of week one, there were 16 clusters, 48 households and 85 cases confirmed.
By day 21, or week three, there were 20 clusters, 86 households and 177 cases from the initial outbreak.