Prevalence of Antibodies to SARS-CoV-2 following natural infection and vaccination in Irish Hospital Healthcare Workers; changing epidemiology as the pandemic progresses

Abstract

BackgroundIn October 2020 SARS-CoV-2 seroprevalence among hospital healthcare workers (HCW) of two Irish hospitals was 15% and 4.1% respectively. We compare seroprevalence in the same HCW population six months later, assess changes in risk factors for seropositivity with progression of the pandemic and serological response to vaccination.MethodsAll staff of both hospitals (N=9038) were invited to participate in an online questionnaire and SARS-CoV-2 antibody testing in April 2021. We measured anti-nucleocapsid and anti-spike antibodies. Frequencies and percentages for positive SARS-CoV-2 antibodies were calculated and adjusted relative risks for participant characteristics were calculated using multivariable regression analysis.Results5085 HCW participated. Seroprevalence increased to 21% and 13% respectively; 26% of infections were previously undiagnosed. Black ethnicity (aRR 1.7, 95% CI 1.3-2.2, p<.001), lower level of education (aRR 1.4 for secondary level education, 95% CI 1.1-1.8, p=0.002), living with other HCW (aRR 1.2, 95% CI 1.0-1.4, p=0.007) were significantly associated with seropositivity. Having direct patient contact also carried a significant risk (being a healthcare assistant (aRR 1.8, 95% CI 1.3-2.3, p<.001), being a nurse (aRR 1.4, 95% CI 1.1-1.5, p=0.022), daily contact with COVID-19 patients (aRR 1.4, 95% CI 1.1-1.7, p=0.002), daily contact with patients without suspected or confirmed COVID-19 (aRR 1.3, 95% CI 1.1- 1.5, p=0.013) Breakthrough infection occurred in 23/4111(0.6%) of fully vaccinated participants; all had anti-S antibodies.ConclusionThe increase in seroprevalence reflects the magnitude of the third wave of the pandemic in Ireland. Genomic sequencing is needed to apportion risk to the workplace versus the household/community. Concerted efforts are needed to mitigate risk factors due to ethnicity and lower level of education, even at this stage of the pandemic. The undiagnosed and breakthrough infections call for ongoing infection prevention and control measures and testing of HCW in the setting of close contact. Vaccinated HCW with confirmed infection should be actively assessed, including SARS-CoV-2 whole genome sequencing (WGS), serology testing and assessment of host determinants, to advance understanding of the reasons for breakthrough infection.

Risk factors for SARS-CoV-2 infection in healthcare workers following an identified nosocomial COVID-19 exposure during waves 1–3 of the pandemic in Ireland

“…Male sex has been identified as a risk factor in HCWs for SARS-CoV-2 seropositivity in a number of studies (2,16,17) with quoted odds ratios ranging from 1.39 to 3.21. The Prevalence of COVID-19 in Irish Healthcare Workers Study, an independent multicentre seroprevalence study of anti-SARS-CoV-2 antibodies in HCWs in Ireland, which included the current study site, found an increased risk of SARS-CoV-2 seropositivity in male HCWs with an aRR 1.2 (95%CI 1.0-1.4, p= 0.016) (13). Studies have demonstrated heterogenous immune responses to SARS-CoV-2 infection in men and women, including delayed peaks in anti-SARS-CoV-2 immunoglobulins in men (18,19), however these findings generally are inconclusive and lack statistical analysis to relate these findings to infectivity or disease severity (20).…”

“…The increased risk observed in other studies may be a reflection of cumulative risk, with certain HCW roles subject to an increased number of exposures over time, increasing the likelihood of infection. Furthermore, nursing staff constitute a significant proportion of many hospitals' total staff numbers (40.1% in the current study site) and this may result in over representation in seroprevalence studies, influencing interpretation of risk (13,14).…”

“…Variability in SARS-CoV-2 infection by job role has been demonstrated in a number of studies, with nursing staff and HCAs (5,6,13,14,30) often cited as being at increased risk of infection. In our findings, no individual job role was determined to have consistently increased risk of infection following a given in-work COVID-19 exposure.…”

“…Dedicated COVID-19 wards were found to be significantly associated with increased likelihood of infection following exposure to an index case (aOR 2.07, 95%CI 1.39-3.08, p < https://doi.org/10.1017/S0950268822001595 Published online by Cambridge University Press 0.001), in comparison to medical wards. Frequent contact with known COVID-19 cases increases risk of infection (13,14,31) and notably, it has been demonstrated that despite adequate access to PPE, this risk persists with daily exposure to COVID-19 cases (1). The cause is likely multi-factorial including high staff turnover in COVID-19 wards leading to increased PPE failures, increased duration of interaction with non-sedated patients and an increased number of high-risk interactions per staff member.…”

A comparative study of eight serological methods shows that spike protein-based ELISAs are the most accurate tests for serodiagnosing SARS-CoV-2 infections in cats and dogs

“…Similar observations have been reported for serological tests employed in humans since S-based assays showed high specificity, contrary to N-based tests, regardless of the IgG isotype targeted. Although the S protein seems to be a specific marker of SARS-CoV-2 in humans (31), this antigen showed no cross reactions with prepandemic sera and sera from cats infected with other coronaviruses, and the detection of false reactors cannot be ruled out. In fact, a few prepandemic dog sera showed a positive result when tested with RBD-S SALUVET ELISA.…”