Study shows 18% of healthcare workers have COVID antibodies

Antibodies to SARS-CoV-2 – the virus which causes COVID-19 – were detected in 18% of healthcare workers in Tallaght University Hospital who participated in a study to evaluate the prevalence of the antibodies.

Dr. Anna Rose Prior
Dr. Anna Rose Prior

Since the onset of the COVID-19 pandemic, healthcare workers are generally considered at higher risk of infection than the general population. This is not only due to patient exposure, but also due to a large number of interactions in the workplace at a time when the general population has reduced social contact. In October 2020, The Health Protection Surveillance Centre reported that 20-25% of all confirmed cases of COVID-19 in Ireland were among healthcare workers.

Over a three month period from mid-July to mid-October the Laboratory Medicine Department in TUH conducted The Tallaght Antibody Study (TAB), to determine what proportion of staff had had COVID-19 at some point since the onset of the pandemic. This was the first Irish study to date to report SARS-CoV-2 seroprevalence of healthcare workers.

Almost 1,200 (943 females (80.2%) and 233 males (19.88%), reflecting the gender breakdown in the hospital employee population, volunteered to participate in the study, which was open to staff from all departments and directorates This represented approximately one third of staff working in the hospital. All data and results were anonymised.

For staff with roles involving more direct patient contact, the rate was 20% and for those with less direct patient the rate was 13%. Before this study, 12% of participants had been diagnosed with COVID-19 at some point, based on a positive swab result. When the group who had known previous infection was excluded, the seroprevalence among those never confirmed to have infection was 7.5%. However over half of this group suspected they had infection at some point.

The initial results of this study indicate that nearly one fifth of staff have antibody evidence of SARS-CoV-2 infection, acquired at some point since the onset of the pandemic. This is higher than the rate of previously known infection in participants. The seroprevalence among the population of healthcare workers is significantly higher than the overall estimated national seroprevalence of 1.7% (as per SCOPI study, conducted by HPSC). It is also significantly higher than that reported by seroprevalence studies from similar healthcare institutions in other countries that implemented similar community restrictions.

Of the group with positive antibodies who were not confirmed previously as having had infection, many of these suspected they possibly had infection as they had symptoms at some point or were known to have been in contact with a case. Some of these had symptoms early in the onset of the pandemic, such as loss of smell and taste, which were not recognised at that point as being due to COVID-19 and so did not meet testing criteria. Staff with fever or respiratory symptoms, such as cough or shortness breath but who were either not tested (because they didn’t meet the criteria at the time) or had a negative result were advised to stay off work until symptoms resolved. Others identified as being a close contact of a case remained off work for 14 days in line with public health advice.

Commenting on the results Dr. Anna Rose Prior, Consultant Microbiologist said, “These results demonstrate that a high proportion of COVID infection in healthcare workers goes undetected and supports the requirement for universal mask use for all patient interactions during the pandemic, both to protect staff but also to minimise the risk of staff unknowingly transmitting infection to patients. This study enables us to identify colleagues who do and don’t develop a measurable immune response to COVID-19. The study is a 12 month study meaning we will follow all participants who want to remain in the study for 12 months, measuring their antibody levels at multiple time points.

“This will give us two key pieces of information, the first is understanding how long a measurable level of antibodies to COVID-19 is present in participants and secondly, how many staff develop antibodies during the coming waves of infection. I would also like to acknowledge the incredible work of the team in Laboratory Medicine who have dedicated their valuable spare time to conduct the study at what is a particularly busy time in the hospital.”

At various times, particularly early in the onset of the pandemic, there were concerns regarding supply and availability of personal protective equipment (PPE). At no point was supply to TUH interrupted and PPE was available at all times. However recommendations around the use of PPE changed at various points.

At the start of the pandemic, before the role of transmission from asymptomatic cases was fully recognised, HCWs wore PPE only when caring for suspected/confirmed cases of COVID-19 in line with guidance at that time. Based on our experience, the use of PPE for all patient interactions was soon mandated in TUH on March 23rd. This was later recommended nationally in April.