Offaly still has by far the highest infection rate in the country, followed by counties Donegal and Dublin, the latest Covid-19 figures show.
The 14-day incidence rate in Offaly is most pronounced in the Tullamore area, where it stands at 823 per 100,000 of population.
However, a walk-in test centre for those without symptoms has meant that more people have been tested in Tullamore than in many other parts of the country.
Dr Una Fallon, Director of Public Health with the HSE in the Midlands, said one of the drivers of this week's figures is testing close contacts of a confirmed case on day ten, particularly household contacts.
Speaking on RTÉ's Morning Ireland, she said about 40% of household contacts of a confirmed B117 case end up becoming cases themselves, compared to around 20% of household contacts during the first and second waves.
"So the day-ten testing of close contacts, on foot of two big outbreaks, is driving the numbers (in Offaly) this week," Dr Fallon said.
"On top of that, we've had the walk-in test centre where we've done approximately 300 tests per day. This has basically doubled the amount of testing in Co Offaly.
"We've tested about 5% of our population in one week, which is enormous. So we are picking up cases that we otherwise wouldn't have detected by that enhanced ascertainment of new cases," said Dr Fallon.