Nurses, doctors, hospital porters; they are frontline in this pandemic. Nearly 1 in 5 of all Covid-19 cases in Ireland has been in healthcare workers.

10,172 have been diagnosed with coronavirus, 4,210 have required hospitalisation and 529 were treated in intensive care.

Now a study of over 1,200 staff in one of Dublin's largest hospitals has found evidence that more staff were infected than actually tested positive for the virus. 

Consultant clinical microbiologist Dr Anna Rose Prior carried out the study at Tallaght Hospital. 

"18% of our staff actually had evidence of prior Covid-19 infection and that compared to a 12% rate of those who had previous confirmed infection."

A third of the hospital took part in the study, including nurses, doctors, and clerical staff. The antibody blood tests were carried out over three months.

Antibodies are a protective protein produced by the immune system. They respond to a foreign substance, like a virus, in order to remove it from the body. 

Those who took part in the study and were found to have antibodies will be monitored into the future.

"We can look at them going forward to see what happens to them, in terms of reinfection rates and re-exposure rates, and see do those antibodies wane."

The HSE is carrying out a similar study. It invited healthcare workers in two large acute hospitals, St James's Hospital, Dublin and University Hospital Galway, to undergo the same testing to determine the presence of Covid-19 antibodies.

The blood tests were carried out over the past two weeks and initial results are expected at the end of November.

The Irish Nurses and Midwives Organisation said it was worried by the findings of the Tallaght Hospital study.

"In older persons services staff are being tested on a repeat, ongoing basis, we think the same needs to happen in the community and in the acute hospital system," said Tony Fitzpatrick, Director of Industrial Relations.

He also called for the 'derogation', where a healthcare service manager can request a person who has been a close contact of someone with Covid-19 to go to work, to be changed.

"A healthcare worker should be treated the same as any other member of the public, follow the public health advice, self isolate and retrict their movements for 14 days. That should apply to healthcare workers as well."

The Tallaght study while offering a clearer picture should not offer any reassurance on immunity to Covid-19.

"We don't want people to have a false reassurance or change their practices to become more lax and think I'm fine now I won't get reinfected.

"We know antibodies do wane, there's one study just today from London that shows that after a short number of months the responses do come down," said microbiolgist, Dr Anna Rose Prior.

"We would hope now that with all the measures we have brought in, more widespread testing, mask wearing for all patient interactions, that hopefully in the future the rate of acquisition of infection would be reduced," said Dr Prior.