Professor Philip Nolan, one of the country’s top Covid experts, has outlined why tests sometimes fail to detect the deadly virus.

Taking to Twitter the chair of the National Public Health Emergency Team Irish Epidemiological Modelling Advisory Group said that there are broadly two reasons why tests may not detect Covid-19.

"First, at any given time, about 30% of infected people are in the latent period, the three to five days after they have been infected, where the virus is multiplying inside their cells and is not yet detectable.

"Second, even when they start to shed the virus, a sensitivity of 70% to 90% means the test will fail to detect the virus in somewhere between 10% and 30% of cases.

Professor Philip Nolan warned that close contacts must continue to isolate even if they return a negative result.

As cases continue to rise in Cork, a Level 3 lockdown could be imposed sometime later this week.

That's according to the Covid advisor to the Irish College of GPs who warned the county it will be seeing tighter measures if things don't change.

Dr Mary Favier said there's a "high possibility" the Rebel county will see a bump up which would mean sports will go back behind closed doors, pubs and restaurants will only be allowed provide outdoor seating, and weddings will be restricted to 25 people.

She told RTE: "It could be as early as next Thursday or Friday.

"We can change what we're all doing, but if we don't I think there's a high possibility we'll join Donegal and Dublin in a level 3."

Yesterday the county saw 36 new cases - a total of 190 cases have been confirmed here so far this week.