SARS-CoV-2 seroprevalence and asymptomatic viral carriage in healthcare workers: a cross-sectional study

Abstract

Objective: To determine the rates of asymptomatic viral carriage and seroprevalence of SARS-CoV-2 antibodies in healthcare workers.

Design: A cross-sectional study of asymptomatic healthcare workers undertaken on 24/25 April 2020.

Setting: University Hospitals Birmingham NHS Foundation Trust (UHBFT), UK.

Participants: 545 asymptomatic healthcare workers were recruited while at work. Participants were invited to participate via the UHBFT social media. Exclusion criteria included current symptoms consistent with COVID-19. No potential participants were excluded.

Intervention: Participants volunteered a nasopharyngeal swab and a venous blood sample that were tested for SARS-CoV-2 RNA and anti-SARS-CoV-2 spike glycoprotein antibodies, respectively. Results were interpreted in the context of prior illnesses and the hospital departments in which participants worked.

Main outcome measure: Proportion of participants demonstrating infection and positive SARS-CoV-2 serology.

Results: The point prevalence of SARS-CoV-2 viral carriage was 2.4% (n=13/545). The overall seroprevalence of SARS-CoV-2 antibodies was 24.4% (n=126/516). Participants who reported prior symptomatic illness had higher seroprevalence (37.5% vs 17.1%, χ²=21.1034, p<0.0001) and quantitatively greater antibody responses than those who had remained asymptomatic. Seroprevalence was greatest among those working in housekeeping (34.5%), acute medicine (33.3%) and general internal medicine (30.3%), with lower rates observed in participants working in intensive care (14.8%). BAME (Black, Asian and minority ethnic) ethnicity was associated with a significantly increased risk of seropositivity (OR: 1.92, 95% CI 1.14 to 3.23, p=0.01). Working on the intensive care unit was associated with a significantly lower risk of seropositivity compared with working in other areas of the hospital (OR: 0.28, 95% CI 0.09 to 0.78, p=0.02).

Conclusions and relevance: We identify differences in the occupational risk of exposure to SARS-CoV-2 between hospital departments and confirm asymptomatic seroconversion occurs in healthcare workers. Further investigation of these observations is required to inform future infection control and occupational health practices.

Keywords: clinical epidemiology; infection control; respiratory infection; viral infection.

Figure 1

(A) Seroprevalence rates in study participants self-reporting prior symptomatic illnesses consistent with COVID-19 compared with asymptomatic individuals. (B) Optical density (OD) of anti-SARS-CoV-2 antibodies in individuals with positive serology classified by self-reported prior symptomatic illness (n=126). Line shows the median value of each group. (C) Timing of prior symptomatic illness in study participants and their relationship with seroprevalence of SARS-CoV-2 antibodies, total inpatients at UHBFT who had tested positive for SARS-CoV-2 by PCR and overall UHBFT-wide deaths in the weeks of March and April 2020. (D) Seroprevalence of SARS-CoV-2 antibody in study participants by department in which they work. AMU, acute medical unit; ED, emergency department; ITU, intensive care unit; OBGYN, obstetrics and gynaecology; OPD, outpatient department; R&D, research and development; UHBFT, University Hospitals Birmingham NHS Foundation Trust.