Those three counties accounted for 64 per cent of all new cases this week.
The CSO also reported that the number of people who have died from Covid-19 is below 10 for the last 10 weeks.
The number of weekly confirmed Covid-19 cases is more than 700 cases in each of the last three weeks up until this week. The median age of new confirmed Covid-19 cases was 32 years old this week.
The week was the third consecutive week that Dublin had more than 300 weekly cases.
It is also the seventeenth week in a row that Longford has recorded less than 10 new cases, and the sixteenth such week for Mayo and Westmeath.
Women and those aged between 25-44 continue to account for the highest number of confirmed cases.
Outbreaks
The CSO said more than half (54 per cent) of confirmed cases are now linked to an outbreak.
For this week, 53 per cent of cases associated with outbreaks are male, 69 per cent are under 44 years old and 49 per cent were located in private houses.
In the last 10 weeks, 11 per cent of cases have been in the 0 – 14 age group and 21 per cent in the 15 – 24 age group.
Health care workers make up 11 per cent of all new cases in the last 10 weeks.
Almost one fifth (19 per cent) of outbreaks affected those aged 80 years and older compared with 14 per cent of all cases. The median age of confirmed cases related to an outbreak is 48.
Dublin, Kildare and Limerick made up 44 per cent of all cases linked to an outbreak this week.
Outbreaks in private houses account for 26 per cent of cases, down from 40 per cent in late March.
